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 $148.91   12.183%   $167.0517   $167.05   $167.05   $167.10  
  Purchase #2 $230.99   11.239%   $256.951   $256.95   $256.95   $257.00  
  Purchase #3 $30.73   10.781%   $34.043   $34.04   $34.05   $34.00  
  Purchase #4 $95.77   6.221%   $101.7279   $101.73   $101.75   $101.70  
  Purchase #5 $74.44   11.695%   $83.1458   $83.15   $83.15   $83.10  
  Purchase #6 $212.90   11.119%   $236.5724   $236.57   $236.55   $236.60  
  Purchase #7 $194.36   12.365%   $218.3926   $218.39   $218.40   $218.40  
  7 purchase totals = $988.10       $1,097.8844   $1,097.88   $1,097.90   $1,097.90