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 $146.91   4.650%   $153.7413   $153.74   $153.75   $153.70  
  Purchase #2 $138.97   8.680%   $151.0326   $151.03   $151.05   $151.00  
  Purchase #3 $116.41   11.852%   $130.2069   $130.21   $130.20   $130.20  
  Purchase #4 $158.59   10.306%   $174.9343   $174.93   $174.95   $174.90  
  Purchase #5 $54.69   7.229%   $58.6435   $58.64   $58.65   $58.60  
  Purchase #6 $187.85   4.321%   $195.967   $195.97   $195.95   $196.00  
  Purchase #7 $108.82   9.473%   $119.1285   $119.13   $119.15   $119.10  
  7 purchase totals = $912.24       $983.6541   $983.65   $983.70   $983.50