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 $40.97   8.673%   $44.5233   $44.52   $44.50   $44.50  
  Purchase #2 $201.43   6.801%   $215.1293   $215.13   $215.15   $215.10  
  Purchase #3 $231.29   8.108%   $250.043   $250.04   $250.05   $250.00  
  Purchase #4 $53.93   11.647%   $60.2112   $60.21   $60.20   $60.20  
  Purchase #5 $204.36   11.108%   $227.0603   $227.06   $227.05   $227.10  
  Purchase #6 $22.49   6.474%   $23.946   $23.95   $23.95   $23.90  
  Purchase #7 $93.51   5.315%   $98.4801   $98.48   $98.50   $98.50  
  7 purchase totals = $847.98       $919.3932   $919.39   $919.40   $919.30