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 $182.48   13.307%   $206.7626   $206.76   $206.75   $206.80  
  Purchase #2 $9.63   13.792%   $10.9582   $10.96   $10.95   $11.00  
  Purchase #3 $58.57   6.831%   $62.5709   $62.57   $62.55   $62.60  
  Purchase #4 $221.94   10.118%   $244.3959   $244.40   $244.40   $244.40  
  Purchase #5 $76.74   10.212%   $84.5767   $84.58   $84.60   $84.60  
  Purchase #6 $78.68   13.144%   $89.0217   $89.02   $89.00   $89.00  
  Purchase #7 $26.48   9.832%   $29.0835   $29.08   $29.10   $29.10  
  7 purchase totals = $654.52       $727.3695   $727.37   $727.35   $727.50