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 $224.70   3.630%   $232.8566   $232.86   $232.85   $232.90  
  Purchase #2 $71.36   4.655%   $74.6818   $74.68   $74.70   $74.70  
  Purchase #3 $151.78   3.347%   $156.8601   $156.86   $156.85   $156.90  
  Purchase #4 $245.62   12.153%   $275.4702   $275.47   $275.45   $275.50  
  Purchase #5 $121.73   12.206%   $136.5884   $136.59   $136.60   $136.60  
  Purchase #6 $125.56   5.142%   $132.0163   $132.02   $132.00   $132.00  
  Purchase #7 $234.48   7.463%   $251.9792   $251.98   $252.00   $252.00  
  7 purchase totals = $1,175.23       $1,260.4526   $1,260.46   $1,260.45   $1,260.60