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 $39.34   7.126%   $42.1434   $42.14   $42.15   $42.10  
  Purchase #2 $165.92   3.669%   $172.0076   $172.01   $172.00   $172.00  
  Purchase #3 $93.75   7.854%   $101.1131   $101.11   $101.10   $101.10  
  Purchase #4 $243.32   7.342%   $261.1846   $261.18   $261.20   $261.20  
  Purchase #5 $188.64   5.126%   $198.3097   $198.31   $198.30   $198.30  
  Purchase #6 $122.91   4.649%   $128.6241   $128.62   $128.60   $128.60  
  Purchase #7 $146.34   13.668%   $166.3418   $166.34   $166.35   $166.30  
  7 purchase totals = $1,000.22       $1,069.7243   $1,069.71   $1,069.70   $1,069.60