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 $84.60   12.770%   $95.4034   $95.40   $95.40   $95.40  
  Purchase #2 $62.61   9.548%   $68.588   $68.59   $68.60   $68.60  
  Purchase #3 $198.57   5.736%   $209.96   $209.96   $209.95   $210.00  
  Purchase #4 $215.35   9.130%   $235.0115   $235.01   $235.00   $235.00  
  Purchase #5 $236.91   11.688%   $264.6   $264.60   $264.60   $264.60  
  Purchase #6 $24.82   3.372%   $25.6569   $25.66   $25.65   $25.70  
  Purchase #7 $17.25   4.738%   $18.0673   $18.07   $18.05   $18.10  
  7 purchase totals = $840.11       $917.2871   $917.29   $917.25   $917.40