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 $244.79   3.866%   $254.2536   $254.25   $254.25   $254.30  
  Purchase #2 $220.90   10.209%   $243.4517   $243.45   $243.45   $243.50  
  Purchase #3 $20.51   9.719%   $22.5034   $22.50   $22.50   $22.50  
  Purchase #4 $65.86   5.592%   $69.5429   $69.54   $69.55   $69.50  
  Purchase #5 $216.70   5.453%   $228.5167   $228.52   $228.50   $228.50  
  Purchase #6 $187.47   7.241%   $201.0447   $201.04   $201.05   $201.00  
  Purchase #7 $27.52   11.283%   $30.6251   $30.63   $30.65   $30.60  
  7 purchase totals = $983.75       $1,049.9381   $1,049.93   $1,049.95   $1,049.90