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 $126.85   11.141%   $140.9824   $140.98   $141.00   $141.00  
  Purchase #2 $22.67   13.798%   $25.798   $25.80   $25.80   $25.80  
  Purchase #3 $46.47   5.869%   $49.1973   $49.20   $49.20   $49.20  
  Purchase #4 $200.71   8.617%   $218.0052   $218.01   $218.00   $218.00  
  Purchase #5 $108.64   6.233%   $115.4115   $115.41   $115.40   $115.40  
  Purchase #6 $216.56   4.630%   $226.5867   $226.59   $226.60   $226.60  
  Purchase #7 $207.33   5.151%   $218.0096   $218.01   $218.00   $218.00  
  7 purchase totals = $929.23       $993.9907   $994.00   $994.00   $994.00