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 $141.99   11.605%   $158.4679   $158.47   $158.45   $158.50  
  Purchase #2 $148.28   10.434%   $163.7515   $163.75   $163.75   $163.80  
  Purchase #3 $103.73   7.776%   $111.796   $111.80   $111.80   $111.80  
  Purchase #4 $217.31   12.837%   $245.2061   $245.21   $245.20   $245.20  
  Purchase #5 $53.29   12.590%   $59.9992   $60.00   $60.00   $60.00  
  Purchase #6 $68.25   8.619%   $74.1325   $74.13   $74.15   $74.10  
  Purchase #7 $185.76   10.455%   $205.1812   $205.18   $205.20   $205.20  
  7 purchase totals = $918.61       $1,018.5344   $1,018.54   $1,018.55   $1,018.60