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 $58.79   11.558%   $65.5849   $65.58   $65.60   $65.60  
  Purchase #2 $186.57   3.857%   $193.766   $193.77   $193.75   $193.80  
  Purchase #3 $72.34   5.157%   $76.0706   $76.07   $76.05   $76.10  
  Purchase #4 $136.52   12.411%   $153.4635   $153.46   $153.45   $153.50  
  Purchase #5 $83.63   4.507%   $87.3992   $87.40   $87.40   $87.40  
  Purchase #6 $39.34   13.257%   $44.5553   $44.56   $44.55   $44.60  
  Purchase #7 $187.82   4.405%   $196.0935   $196.09   $196.10   $196.10  
  7 purchase totals = $765.01       $816.9330   $816.93   $816.90   $817.10