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 $56.56   4.772%   $59.259   $59.26   $59.25   $59.30  
  Purchase #2 $46.70   10.864%   $51.7735   $51.77   $51.75   $51.80  
  Purchase #3 $55.87   7.576%   $60.1027   $60.10   $60.10   $60.10  
  Purchase #4 $147.62   4.264%   $153.9145   $153.91   $153.90   $153.90  
  Purchase #5 $84.94   9.502%   $93.011   $93.01   $93.00   $93.00  
  Purchase #6 $116.57   13.354%   $132.1368   $132.14   $132.15   $132.10  
  Purchase #7 $142.89   4.647%   $149.5301   $149.53   $149.55   $149.50  
  7 purchase totals = $651.15       $699.7276   $699.72   $699.70   $699.70