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 $224.84   12.752%   $253.5116   $253.51   $253.50   $253.50  
  Purchase #2 $229.49   5.677%   $242.5181   $242.52   $242.50   $242.50  
  Purchase #3 $30.64   6.640%   $32.6745   $32.67   $32.65   $32.70  
  Purchase #4 $203.29   12.395%   $228.4878   $228.49   $228.50   $228.50  
  Purchase #5 $173.46   5.377%   $182.7869   $182.79   $182.80   $182.80  
  Purchase #6 $248.85   7.475%   $267.4515   $267.45   $267.45   $267.50  
  Purchase #7 $217.53   11.291%   $242.0913   $242.09   $242.10   $242.10  
  7 purchase totals = $1,328.10       $1,449.5217   $1,449.52   $1,449.50   $1,449.60