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 $30.56   5.304%   $32.1809   $32.18   $32.20   $32.20  
  Purchase #2 $183.43   10.667%   $202.9965   $203.00   $203.00   $203.00  
  Purchase #3 $158.34   11.745%   $176.937   $176.94   $176.95   $176.90  
  Purchase #4 $200.94   7.358%   $215.7252   $215.73   $215.75   $215.70  
  Purchase #5 $240.91   7.760%   $259.6046   $259.60   $259.60   $259.60  
  Purchase #6 $248.95   9.777%   $273.2898   $273.29   $273.30   $273.30  
  Purchase #7 $21.66   5.599%   $22.8727   $22.87   $22.85   $22.90  
  7 purchase totals = $1,084.79       $1,183.6067   $1,183.61   $1,183.65   $1,183.60