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 $64.44   3.716%   $66.8346   $66.83   $66.85   $66.80  
  Purchase #2 $137.84   13.156%   $155.9742   $155.97   $155.95   $156.00  
  Purchase #3 $113.60   13.795%   $129.2711   $129.27   $129.25   $129.30  
  Purchase #4 $110.51   12.697%   $124.5415   $124.54   $124.55   $124.50  
  Purchase #5 $148.53   8.662%   $161.3957   $161.40   $161.40   $161.40  
  Purchase #6 $152.55   13.115%   $172.5569   $172.56   $172.55   $172.60  
  Purchase #7 $69.91   7.343%   $75.0435   $75.04   $75.05   $75.00  
  7 purchase totals = $797.38       $885.6175   $885.61   $885.60   $885.60