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 $119.79   5.241%   $126.0682   $126.07   $126.05   $126.10  
  Purchase #2 $78.61   11.517%   $87.6635   $87.66   $87.65   $87.70  
  Purchase #3 $161.51   6.829%   $172.5395   $172.54   $172.55   $172.50  
  Purchase #4 $51.59   13.468%   $58.5381   $58.54   $58.55   $58.50  
  Purchase #5 $13.74   6.220%   $14.5946   $14.59   $14.60   $14.60  
  Purchase #6 $182.33   8.285%   $197.436   $197.44   $197.45   $197.40  
  Purchase #7 $173.36   12.745%   $195.4547   $195.45   $195.45   $195.50  
  7 purchase totals = $780.93       $852.2946   $852.29   $852.30   $852.30