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 $153.99   5.759%   $162.8583   $162.86   $162.85   $162.90  
  Purchase #2 $238.80   12.676%   $269.0703   $269.07   $269.05   $269.10  
  Purchase #3 $229.28   7.856%   $247.2922   $247.29   $247.30   $247.30  
  Purchase #4 $56.68   12.840%   $63.9577   $63.96   $63.95   $64.00  
  Purchase #5 $83.37   12.774%   $94.0197   $94.02   $94.00   $94.00  
  Purchase #6 $84.60   3.108%   $87.2294   $87.23   $87.25   $87.20  
  Purchase #7 $67.62   5.126%   $71.0862   $71.09   $71.10   $71.10  
  7 purchase totals = $914.34       $995.5138   $995.52   $995.50   $995.60