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 $194.66   8.521%   $211.247   $211.25   $211.25   $211.20  
  Purchase #2 $60.97   12.686%   $68.7047   $68.70   $68.70   $68.70  
  Purchase #3 $115.28   7.471%   $123.8926   $123.89   $123.90   $123.90  
  Purchase #4 $199.75   12.748%   $225.2141   $225.21   $225.20   $225.20  
  Purchase #5 $116.78   7.501%   $125.5397   $125.54   $125.55   $125.50  
  Purchase #6 $21.43   12.451%   $24.0982   $24.10   $24.10   $24.10  
  Purchase #7 $118.57   9.472%   $129.801   $129.80   $129.80   $129.80  
  7 purchase totals = $827.44       $908.4973   $908.49   $908.50   $908.40