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 $205.81   11.632%   $229.7498   $229.75   $229.75   $229.70  
  Purchase #2 $67.82   8.309%   $73.4552   $73.46   $73.45   $73.50  
  Purchase #3 $151.99   8.774%   $165.3256   $165.33   $165.35   $165.30  
  Purchase #4 $207.38   6.153%   $220.1401   $220.14   $220.15   $220.10  
  Purchase #5 $43.66   11.203%   $48.5512   $48.55   $48.55   $48.60  
  Purchase #6 $94.93   8.388%   $102.8927   $102.89   $102.90   $102.90  
  Purchase #7 $31.42   6.425%   $33.4387   $33.44   $33.45   $33.40  
  7 purchase totals = $803.01       $873.5533   $873.56   $873.60   $873.50