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 $235.94   11.706%   $263.5591   $263.56   $263.55   $263.60  
  Purchase #2 $238.65   12.281%   $267.9586   $267.96   $267.95   $268.00  
  Purchase #3 $90.37   4.494%   $94.4312   $94.43   $94.45   $94.40  
  Purchase #4 $105.54   8.168%   $114.1605   $114.16   $114.15   $114.20  
  Purchase #5 $160.57   9.352%   $175.5865   $175.59   $175.60   $175.60  
  Purchase #6 $9.87   3.596%   $10.2249   $10.22   $10.20   $10.20  
  Purchase #7 $15.86   3.323%   $16.387   $16.39   $16.40   $16.40  
  7 purchase totals = $856.80       $942.3078   $942.31   $942.30   $942.40