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 $56.25   5.874%   $59.5541   $59.55   $59.55   $59.60  
  Purchase #2 $187.80   6.117%   $199.2877   $199.29   $199.30   $199.30  
  Purchase #3 $211.57   11.679%   $236.2793   $236.28   $236.30   $236.30  
  Purchase #4 $68.82   7.584%   $74.0393   $74.04   $74.05   $74.00  
  Purchase #5 $86.73   12.544%   $97.6094   $97.61   $97.60   $97.60  
  Purchase #6 $199.93   9.107%   $218.1376   $218.14   $218.15   $218.10  
  Purchase #7 $6.86   12.721%   $7.7327   $7.73   $7.75   $7.70  
  7 purchase totals = $817.96       $892.6401   $892.64   $892.70   $892.60