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 $66.79   11.120%   $74.217   $74.22   $74.20   $74.20  
  Purchase #2 $96.53   8.738%   $104.9648   $104.96   $104.95   $105.00  
  Purchase #3 $125.41   3.383%   $129.6526   $129.65   $129.65   $129.70  
  Purchase #4 $24.88   9.520%   $27.2486   $27.25   $27.25   $27.20  
  Purchase #5 $48.38   10.386%   $53.4047   $53.40   $53.40   $53.40  
  Purchase #6 $5.38   13.268%   $6.0938   $6.09   $6.10   $6.10  
  Purchase #7 $214.40   9.514%   $234.798   $234.80   $234.80   $234.80  
  7 purchase totals = $581.77       $630.3795   $630.37   $630.35   $630.40