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 $57.66   3.385%   $59.6118   $59.61   $59.60   $59.60  
  Purchase #2 $216.62   5.396%   $228.3088   $228.31   $228.30   $228.30  
  Purchase #3 $222.60   6.105%   $236.1897   $236.19   $236.20   $236.20  
  Purchase #4 $67.70   7.276%   $72.6259   $72.63   $72.65   $72.60  
  Purchase #5 $79.50   6.783%   $84.8925   $84.89   $84.90   $84.90  
  Purchase #6 $76.33   5.816%   $80.7694   $80.77   $80.75   $80.80  
  Purchase #7 $140.62   9.222%   $153.588   $153.59   $153.60   $153.60  
  7 purchase totals = $861.03       $915.9861   $915.99   $916.00   $916.00