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 $102.97   11.329%   $114.6355   $114.64   $114.65   $114.60  
  Purchase #2 $56.96   5.344%   $60.0039   $60.00   $60.00   $60.00  
  Purchase #3 $177.92   8.216%   $192.5379   $192.54   $192.55   $192.50  
  Purchase #4 $102.49   8.266%   $110.9618   $110.96   $110.95   $111.00  
  Purchase #5 $131.63   9.736%   $144.4455   $144.45   $144.45   $144.40  
  Purchase #6 $91.86   9.679%   $100.7511   $100.75   $100.75   $100.80  
  Purchase #7 $62.34   9.439%   $68.2243   $68.22   $68.20   $68.20  
  7 purchase totals = $726.17       $791.5600   $791.56   $791.55   $791.50