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 $217.98   11.388%   $242.8036   $242.80   $242.80   $242.80  
  Purchase #2 $102.72   4.846%   $107.6978   $107.70   $107.70   $107.70  
  Purchase #3 $161.87   8.196%   $175.1369   $175.14   $175.15   $175.10  
  Purchase #4 $57.75   7.697%   $62.195   $62.20   $62.20   $62.20  
  Purchase #5 $81.93   12.415%   $92.1016   $92.10   $92.10   $92.10  
  Purchase #6 $201.73   9.244%   $220.3779   $220.38   $220.40   $220.40  
  Purchase #7 $32.61   6.817%   $34.833   $34.83   $34.85   $34.80  
  7 purchase totals = $856.59       $935.1458   $935.15   $935.20   $935.10