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 $68.68   6.426%   $73.0934   $73.09   $73.10   $73.10  
  Purchase #2 $69.88   7.185%   $74.9009   $74.90   $74.90   $74.90  
  Purchase #3 $60.77   11.767%   $67.9208   $67.92   $67.90   $67.90  
  Purchase #4 $169.38   5.209%   $178.203   $178.20   $178.20   $178.20  
  Purchase #5 $246.56   10.174%   $271.645   $271.65   $271.65   $271.60  
  Purchase #6 $10.60   10.390%   $11.7013   $11.70   $11.70   $11.70  
  Purchase #7 $130.41   8.702%   $141.7583   $141.76   $141.75   $141.80  
  7 purchase totals = $756.28       $819.2227   $819.22   $819.20   $819.20