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 $213.70   11.713%   $238.7307   $238.73   $238.75   $238.70  
  Purchase #2 $223.68   13.630%   $254.1676   $254.17   $254.15   $254.20  
  Purchase #3 $167.95   5.216%   $176.7103   $176.71   $176.70   $176.70  
  Purchase #4 $129.63   13.847%   $147.5799   $147.58   $147.60   $147.60  
  Purchase #5 $207.78   11.725%   $232.1422   $232.14   $232.15   $232.10  
  Purchase #6 $129.34   5.578%   $136.5546   $136.55   $136.55   $136.60  
  Purchase #7 $22.91   8.531%   $24.8645   $24.86   $24.85   $24.90  
  7 purchase totals = $1,094.99       $1,210.7498   $1,210.74   $1,210.75   $1,210.80