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 $240.67   5.180%   $253.1367   $253.14   $253.15   $253.10  
  Purchase #2 $241.86   13.179%   $273.7347   $273.73   $273.75   $273.70  
  Purchase #3 $51.45   8.828%   $55.992   $55.99   $56.00   $56.00  
  Purchase #4 $123.35   8.343%   $133.6411   $133.64   $133.65   $133.60  
  Purchase #5 $167.94   8.429%   $182.0957   $182.10   $182.10   $182.10  
  Purchase #6 $45.57   9.202%   $49.7634   $49.76   $49.75   $49.80  
  Purchase #7 $101.74   13.175%   $115.1442   $115.14   $115.15   $115.10  
  7 purchase totals = $972.58       $1,063.5078   $1,063.50   $1,063.55   $1,063.40