Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $184.99   12.291%   $207.7271   $207.73   $207.75   $207.70  
  Purchase #2 $115.60   3.387%   $119.5154   $119.52   $119.50   $119.50  
  Purchase #3 $233.45   13.470%   $264.8957   $264.90   $264.90   $264.90  
  Purchase #4 $194.86   3.431%   $201.5456   $201.55   $201.55   $201.50  
  Purchase #5 $165.95   5.217%   $174.6076   $174.61   $174.60   $174.60  
  Purchase #6 $180.71   5.594%   $190.8189   $190.82   $190.80   $190.80  
  Purchase #7 $189.28   13.729%   $215.2663   $215.27   $215.25   $215.30  
  7 purchase totals = $1,264.84       $1,374.3766   $1,374.40   $1,374.35   $1,374.30