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 $194.29   3.751%   $201.5778   $201.58   $201.60   $201.60  
  Purchase #2 $118.93   3.866%   $123.5278   $123.53   $123.55   $123.50  
  Purchase #3 $57.49   8.154%   $62.1777   $62.18   $62.20   $62.20  
  Purchase #4 $75.31   7.522%   $80.9748   $80.97   $80.95   $81.00  
  Purchase #5 $165.88   4.843%   $173.9136   $173.91   $173.90   $173.90  
  Purchase #6 $127.55   10.540%   $140.9938   $140.99   $141.00   $141.00  
  Purchase #7 $155.64   10.754%   $172.3775   $172.38   $172.40   $172.40  
  7 purchase totals = $895.09       $955.5430   $955.54   $955.60   $955.60