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 $214.98   11.373%   $239.4297   $239.43   $239.45   $239.40  
  Purchase #2 $143.85   11.182%   $159.9353   $159.94   $159.95   $159.90  
  Purchase #3 $115.83   5.717%   $122.452   $122.45   $122.45   $122.50  
  Purchase #4 $242.83   10.301%   $267.8439   $267.84   $267.85   $267.80  
  Purchase #5 $155.43   12.742%   $175.2349   $175.23   $175.25   $175.20  
  Purchase #6 $11.57   5.802%   $12.2413   $12.24   $12.25   $12.20  
  Purchase #7 $75.25   11.405%   $83.8323   $83.83   $83.85   $83.80  
  7 purchase totals = $959.74       $1,060.9694   $1,060.96   $1,061.05   $1,060.80