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 $89.96   7.826%   $97.0003   $97.00   $97.00   $97.00  
  Purchase #2 $101.73   11.718%   $113.6507   $113.65   $113.65   $113.70  
  Purchase #3 $44.88   3.707%   $46.5437   $46.54   $46.55   $46.50  
  Purchase #4 $199.56   3.361%   $206.2672   $206.27   $206.25   $206.30  
  Purchase #5 $165.52   11.201%   $184.0599   $184.06   $184.05   $184.10  
  Purchase #6 $115.67   7.134%   $123.9219   $123.92   $123.90   $123.90  
  Purchase #7 $60.70   9.741%   $66.6128   $66.61   $66.60   $66.60  
  7 purchase totals = $778.02       $838.0565   $838.05   $838.00   $838.10