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 $119.29   11.556%   $133.0752   $133.08   $133.10   $133.10  
  Purchase #2 $35.84   4.154%   $37.3288   $37.33   $37.35   $37.30  
  Purchase #3 $94.86   5.221%   $99.8126   $99.81   $99.80   $99.80  
  Purchase #4 $217.73   8.793%   $236.875   $236.88   $236.90   $236.90  
  Purchase #5 $112.76   4.859%   $118.239   $118.24   $118.25   $118.20  
  Purchase #6 $233.76   5.374%   $246.3223   $246.32   $246.30   $246.30  
  Purchase #7 $13.47   8.465%   $14.6102   $14.61   $14.60   $14.60  
  7 purchase totals = $827.71       $886.2631   $886.27   $886.30   $886.20