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 $19.34   4.500%   $20.2103   $20.21   $20.20   $20.20  
  Purchase #2 $237.36   12.317%   $266.5956   $266.60   $266.60   $266.60  
  Purchase #3 $54.54   10.699%   $60.3752   $60.38   $60.40   $60.40  
  Purchase #4 $111.45   10.479%   $123.1288   $123.13   $123.15   $123.10  
  Purchase #5 $196.90   8.616%   $213.8649   $213.86   $213.85   $213.90  
  Purchase #6 $5.50   12.275%   $6.1751   $6.18   $6.20   $6.20  
  Purchase #7 $8.74   12.403%   $9.824   $9.82   $9.80   $9.80  
  7 purchase totals = $633.83       $700.1739   $700.18   $700.20   $700.20