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 $61.48   8.639%   $66.7913   $66.79   $66.80   $66.80  
  Purchase #2 $83.98   12.148%   $94.1819   $94.18   $94.20   $94.20  
  Purchase #3 $167.95   13.152%   $190.0388   $190.04   $190.05   $190.00  
  Purchase #4 $76.49   9.212%   $83.5363   $83.54   $83.55   $83.50  
  Purchase #5 $83.77   11.375%   $93.2988   $93.30   $93.30   $93.30  
  Purchase #6 $192.92   9.692%   $211.6178   $211.62   $211.60   $211.60  
  Purchase #7 $151.34   10.391%   $167.0657   $167.07   $167.05   $167.10  
  7 purchase totals = $817.93       $906.5306   $906.54   $906.55   $906.50