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 $143.37   9.489%   $156.9744   $156.97   $156.95   $157.00  
  Purchase #2 $34.80   4.468%   $36.3549   $36.35   $36.35   $36.40  
  Purchase #3 $140.29   8.744%   $152.557   $152.56   $152.55   $152.60  
  Purchase #4 $114.27   4.205%   $119.0751   $119.08   $119.10   $119.10  
  Purchase #5 $73.34   13.692%   $83.3817   $83.38   $83.40   $83.40  
  Purchase #6 $140.67   4.395%   $146.8524   $146.85   $146.85   $146.90  
  Purchase #7 $225.91   13.408%   $256.2   $256.20   $256.20   $256.20  
  7 purchase totals = $872.65       $951.3955   $951.39   $951.40   $951.60