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 $150.72   7.798%   $162.4731   $162.47   $162.45   $162.50  
  Purchase #2 $78.29   7.791%   $84.3896   $84.39   $84.40   $84.40  
  Purchase #3 $177.78   9.591%   $194.8309   $194.83   $194.85   $194.80  
  Purchase #4 $133.99   3.753%   $139.0186   $139.02   $139.00   $139.00  
  Purchase #5 $17.70   12.515%   $19.9152   $19.92   $19.90   $19.90  
  Purchase #6 $158.27   7.485%   $170.1165   $170.12   $170.10   $170.10  
  Purchase #7 $141.57   5.342%   $149.1327   $149.13   $149.15   $149.10  
  7 purchase totals = $858.32       $919.8766   $919.88   $919.85   $919.80