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 $186.93   10.591%   $206.7278   $206.73   $206.75   $206.70  
  Purchase #2 $46.72   13.493%   $53.0239   $53.02   $53.00   $53.00  
  Purchase #3 $183.38   9.740%   $201.2412   $201.24   $201.25   $201.20  
  Purchase #4 $109.35   9.695%   $119.9515   $119.95   $119.95   $120.00  
  Purchase #5 $140.68   12.662%   $158.4929   $158.49   $158.50   $158.50  
  Purchase #6 $69.61   8.228%   $75.3375   $75.34   $75.35   $75.30  
  Purchase #7 $206.94   12.401%   $232.6026   $232.60   $232.60   $232.60  
  7 purchase totals = $943.61       $1,047.3774   $1,047.37   $1,047.40   $1,047.30