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 $241.61   5.429%   $254.727   $254.73   $254.75   $254.70  
  Purchase #2 $158.78   11.819%   $177.5462   $177.55   $177.55   $177.50  
  Purchase #3 $17.26   13.861%   $19.6524   $19.65   $19.65   $19.70  
  Purchase #4 $210.74   11.256%   $234.4609   $234.46   $234.45   $234.50  
  Purchase #5 $159.25   3.709%   $165.1566   $165.16   $165.15   $165.20  
  Purchase #6 $60.79   6.147%   $64.5268   $64.53   $64.55   $64.50  
  Purchase #7 $218.60   10.839%   $242.2941   $242.29   $242.30   $242.30  
  7 purchase totals = $1,067.03       $1,158.3640   $1,158.37   $1,158.40   $1,158.40