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 $93.47   9.167%   $102.0384   $102.04   $102.05   $102.00  
  Purchase #2 $56.56   13.562%   $64.2307   $64.23   $64.25   $64.20  
  Purchase #3 $64.46   6.424%   $68.6009   $68.60   $68.60   $68.60  
  Purchase #4 $139.36   9.133%   $152.0877   $152.09   $152.10   $152.10  
  Purchase #5 $113.55   3.532%   $117.5606   $117.56   $117.55   $117.60  
  Purchase #6 $236.36   11.742%   $264.1134   $264.11   $264.10   $264.10  
  Purchase #7 $80.38   5.297%   $84.6377   $84.64   $84.65   $84.60  
  7 purchase totals = $784.14       $853.2694   $853.27   $853.30   $853.20