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 $226.79   7.784%   $244.4433   $244.44   $244.45   $244.40  
  Purchase #2 $224.73   13.326%   $254.6775   $254.68   $254.70   $254.70  
  Purchase #3 $62.33   10.592%   $68.932   $68.93   $68.95   $68.90  
  Purchase #4 $92.93   11.321%   $103.4506   $103.45   $103.45   $103.50  
  Purchase #5 $162.53   7.527%   $174.7636   $174.76   $174.75   $174.80  
  Purchase #6 $201.88   9.787%   $221.638   $221.64   $221.65   $221.60  
  Purchase #7 $189.36   13.143%   $214.2476   $214.25   $214.25   $214.20  
  7 purchase totals = $1,160.55       $1,282.1526   $1,282.15   $1,282.20   $1,282.10