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 $167.96   10.283%   $185.2313   $185.23   $185.25   $185.20  
  Purchase #2 $187.77   4.253%   $195.7559   $195.76   $195.75   $195.80  
  Purchase #3 $53.91   9.545%   $59.0557   $59.06   $59.05   $59.10  
  Purchase #4 $66.78   11.676%   $74.5772   $74.58   $74.60   $74.60  
  Purchase #5 $57.27   6.736%   $61.1277   $61.13   $61.15   $61.10  
  Purchase #6 $205.38   3.209%   $211.9706   $211.97   $211.95   $212.00  
  Purchase #7 $179.47   5.305%   $188.9909   $188.99   $189.00   $189.00  
  7 purchase totals = $918.54       $976.7093   $976.72   $976.75   $976.80