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 $187.53   8.756%   $203.9501   $203.95   $203.95   $204.00  
  Purchase #2 $48.54   10.324%   $53.5513   $53.55   $53.55   $53.60  
  Purchase #3 $191.43   13.432%   $217.1429   $217.14   $217.15   $217.10  
  Purchase #4 $235.26   4.736%   $246.4019   $246.40   $246.40   $246.40  
  Purchase #5 $79.78   4.561%   $83.4188   $83.42   $83.40   $83.40  
  Purchase #6 $238.94   12.546%   $268.9174   $268.92   $268.90   $268.90  
  Purchase #7 $226.55   7.535%   $243.6205   $243.62   $243.60   $243.60  
  7 purchase totals = $1,208.03       $1,317.0029   $1,317.00   $1,316.95   $1,317.00