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 $220.34   10.843%   $244.2315   $244.23   $244.25   $244.20  
  Purchase #2 $232.90   9.624%   $255.3143   $255.31   $255.30   $255.30  
  Purchase #3 $81.66   9.678%   $89.5631   $89.56   $89.55   $89.60  
  Purchase #4 $161.62   9.695%   $177.2891   $177.29   $177.30   $177.30  
  Purchase #5 $132.63   5.599%   $140.056   $140.06   $140.05   $140.10  
  Purchase #6 $127.86   6.281%   $135.8909   $135.89   $135.90   $135.90  
  Purchase #7 $193.63   10.518%   $213.996   $214.00   $214.00   $214.00  
  7 purchase totals = $1,150.64       $1,256.3409   $1,256.34   $1,256.35   $1,256.40