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 $248.98   10.540%   $275.2225   $275.22   $275.20   $275.20  
  Purchase #2 $41.88   10.353%   $46.2158   $46.22   $46.20   $46.20  
  Purchase #3 $215.72   11.525%   $240.5817   $240.58   $240.60   $240.60  
  Purchase #4 $232.44   13.273%   $263.2918   $263.29   $263.30   $263.30  
  Purchase #5 $18.96   10.507%   $20.9521   $20.95   $20.95   $21.00  
  Purchase #6 $23.81   3.149%   $24.5598   $24.56   $24.55   $24.60  
  Purchase #7 $68.38   6.526%   $72.8425   $72.84   $72.85   $72.80  
  7 purchase totals = $850.17       $943.6662   $943.66   $943.65   $943.70