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 $44.42   12.615%   $50.0236   $50.02   $50.00   $50.00  
  Purchase #2 $62.38   4.220%   $65.0124   $65.01   $65.00   $65.00  
  Purchase #3 $13.60   6.772%   $14.521   $14.52   $14.50   $14.50  
  Purchase #4 $86.25   5.310%   $90.8299   $90.83   $90.85   $90.80  
  Purchase #5 $221.78   7.761%   $238.9923   $238.99   $239.00   $239.00  
  Purchase #6 $211.50   8.635%   $229.763   $229.76   $229.75   $229.80  
  Purchase #7 $221.33   6.479%   $235.67   $235.67   $235.65   $235.70  
  7 purchase totals = $861.26       $924.8122   $924.80   $924.75   $924.80