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 $236.27   9.756%   $259.3205   $259.32   $259.30   $259.30  
  Purchase #2 $36.37   13.699%   $41.3523   $41.35   $41.35   $41.40  
  Purchase #3 $111.51   12.138%   $125.0451   $125.05   $125.05   $125.00  
  Purchase #4 $184.50   6.182%   $195.9058   $195.91   $195.90   $195.90  
  Purchase #5 $55.27   13.523%   $62.7442   $62.74   $62.75   $62.70  
  Purchase #6 $70.30   6.818%   $75.0931   $75.09   $75.10   $75.10  
  Purchase #7 $206.54   8.201%   $223.4783   $223.48   $223.50   $223.50  
  7 purchase totals = $900.76       $982.9393   $982.94   $982.95   $982.90