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 $50.51   7.404%   $54.2498   $54.25   $54.25   $54.20  
  Purchase #2 $248.71   13.374%   $281.9725   $281.97   $281.95   $282.00  
  Purchase #3 $113.29   11.239%   $126.0227   $126.02   $126.00   $126.00  
  Purchase #4 $153.68   12.553%   $172.9715   $172.97   $172.95   $173.00  
  Purchase #5 $88.34   6.499%   $94.0812   $94.08   $94.10   $94.10  
  Purchase #6 $187.95   13.822%   $213.9284   $213.93   $213.95   $213.90  
  Purchase #7 $169.38   9.170%   $184.9121   $184.91   $184.90   $184.90  
  7 purchase totals = $1,011.86       $1,128.1382   $1,128.13   $1,128.10   $1,128.10