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 $82.55   6.734%   $88.1089   $88.11   $88.10   $88.10  
  Purchase #2 $197.53   11.858%   $220.9531   $220.95   $220.95   $221.00  
  Purchase #3 $137.89   11.464%   $153.6977   $153.70   $153.70   $153.70  
  Purchase #4 $56.44   13.455%   $64.034   $64.03   $64.05   $64.00  
  Purchase #5 $248.39   11.284%   $276.4183   $276.42   $276.40   $276.40  
  Purchase #6 $194.98   3.509%   $201.8218   $201.82   $201.80   $201.80  
  Purchase #7 $43.65   10.420%   $48.1983   $48.20   $48.20   $48.20  
  7 purchase totals = $961.43       $1,053.2321   $1,053.23   $1,053.20   $1,053.20