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 $83.79   10.492%   $92.5812   $92.58   $92.60   $92.60  
  Purchase #2 $196.63   5.625%   $207.6904   $207.69   $207.70   $207.70  
  Purchase #3 $146.45   8.497%   $158.8939   $158.89   $158.90   $158.90  
  Purchase #4 $134.57   13.582%   $152.8473   $152.85   $152.85   $152.80  
  Purchase #5 $95.62   6.372%   $101.7129   $101.71   $101.70   $101.70  
  Purchase #6 $243.31   6.759%   $259.7553   $259.76   $259.75   $259.80  
  Purchase #7 $206.97   9.783%   $227.2179   $227.22   $227.20   $227.20  
  7 purchase totals = $1,107.34       $1,200.6989   $1,200.70   $1,200.70   $1,200.70