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 $87.85   11.572%   $98.016   $98.02   $98.00   $98.00  
  Purchase #2 $142.38   6.758%   $152.002   $152.00   $152.00   $152.00  
  Purchase #3 $139.94   6.482%   $149.0109   $149.01   $149.00   $149.00  
  Purchase #4 $180.43   5.309%   $190.009   $190.01   $190.00   $190.00  
  Purchase #5 $233.93   5.776%   $247.4418   $247.44   $247.45   $247.40  
  Purchase #6 $25.31   8.110%   $27.3626   $27.36   $27.35   $27.40  
  Purchase #7 $147.57   11.725%   $164.8726   $164.87   $164.85   $164.90  
  7 purchase totals = $957.41       $1,028.7149   $1,028.71   $1,028.65   $1,028.70