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 $237.47   5.282%   $250.0132   $250.01   $250.00   $250.00  
  Purchase #2 $62.32   5.868%   $65.9769   $65.98   $66.00   $66.00  
  Purchase #3 $24.48   13.756%   $27.8475   $27.85   $27.85   $27.80  
  Purchase #4 $231.34   12.722%   $260.7711   $260.77   $260.75   $260.80  
  Purchase #5 $72.79   8.734%   $79.1475   $79.15   $79.15   $79.10  
  Purchase #6 $150.58   4.274%   $157.0158   $157.02   $157.00   $157.00  
  Purchase #7 $210.39   6.710%   $224.5072   $224.51   $224.50   $224.50  
  7 purchase totals = $989.37       $1,065.2792   $1,065.29   $1,065.25   $1,065.20