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 $87.40   12.736%   $98.5313   $98.53   $98.55   $98.50  
  Purchase #2 $96.86   9.694%   $106.2496   $106.25   $106.25   $106.20  
  Purchase #3 $166.88   11.370%   $185.8543   $185.85   $185.85   $185.90  
  Purchase #4 $136.77   5.751%   $144.6356   $144.64   $144.65   $144.60  
  Purchase #5 $78.51   11.664%   $87.6674   $87.67   $87.65   $87.70  
  Purchase #6 $220.78   4.675%   $231.1015   $231.10   $231.10   $231.10  
  Purchase #7 $84.79   7.604%   $91.2374   $91.24   $91.25   $91.20  
  7 purchase totals = $871.99       $945.2771   $945.28   $945.30   $945.20