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 $76.64   10.611%   $84.7723   $84.77   $84.75   $84.80  
  Purchase #2 $131.90   12.749%   $148.7159   $148.72   $148.70   $148.70  
  Purchase #3 $82.44   5.519%   $86.9899   $86.99   $87.00   $87.00  
  Purchase #4 $242.78   4.492%   $253.6857   $253.69   $253.70   $253.70  
  Purchase #5 $8.82   7.468%   $9.4787   $9.48   $9.50   $9.50  
  Purchase #6 $231.31   7.512%   $248.686   $248.69   $248.70   $248.70  
  Purchase #7 $215.65   5.415%   $227.3274   $227.33   $227.35   $227.30  
  7 purchase totals = $989.54       $1,059.6559   $1,059.67   $1,059.70   $1,059.70