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 $113.99   4.413%   $119.0204   $119.02   $119.00   $119.00  
  Purchase #2 $11.80   10.428%   $13.0305   $13.03   $13.05   $13.00  
  Purchase #3 $66.94   11.106%   $74.3744   $74.37   $74.35   $74.40  
  Purchase #4 $151.39   11.818%   $169.2813   $169.28   $169.30   $169.30  
  Purchase #5 $91.91   5.480%   $96.9467   $96.95   $96.95   $96.90  
  Purchase #6 $206.92   7.163%   $221.7417   $221.74   $221.75   $221.70  
  Purchase #7 $150.89   8.478%   $163.6825   $163.68   $163.70   $163.70  
  7 purchase totals = $793.84       $858.0775   $858.07   $858.10   $858.00