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 $226.45   7.497%   $243.427   $243.43   $243.45   $243.40  
  Purchase #2 $166.83   13.662%   $189.6223   $189.62   $189.60   $189.60  
  Purchase #3 $28.70   11.546%   $32.0137   $32.01   $32.00   $32.00  
  Purchase #4 $19.51   7.111%   $20.8974   $20.90   $20.90   $20.90  
  Purchase #5 $125.74   12.269%   $141.167   $141.17   $141.15   $141.20  
  Purchase #6 $51.85   7.727%   $55.8564   $55.86   $55.85   $55.90  
  Purchase #7 $96.42   13.347%   $109.2892   $109.29   $109.30   $109.30  
  7 purchase totals = $715.50       $792.2730   $792.28   $792.25   $792.30