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 $113.71   10.235%   $125.3482   $125.35   $125.35   $125.30  
  Purchase #2 $234.97   13.245%   $266.0918   $266.09   $266.10   $266.10  
  Purchase #3 $211.89   7.733%   $228.2755   $228.28   $228.30   $228.30  
  Purchase #4 $67.94   12.338%   $76.3224   $76.32   $76.30   $76.30  
  Purchase #5 $141.32   6.184%   $150.0592   $150.06   $150.05   $150.10  
  Purchase #6 $75.86   4.516%   $79.2858   $79.29   $79.30   $79.30  
  Purchase #7 $33.61   13.148%   $38.029   $38.03   $38.05   $38.00  
  7 purchase totals = $879.30       $963.4119   $963.42   $963.45   $963.40