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 $148.30   11.723%   $165.6852   $165.69   $165.70   $165.70  
  Purchase #2 $86.99   10.189%   $95.8534   $95.85   $95.85   $95.90  
  Purchase #3 $59.63   4.757%   $62.4666   $62.47   $62.45   $62.50  
  Purchase #4 $168.95   6.725%   $180.3119   $180.31   $180.30   $180.30  
  Purchase #5 $229.64   9.640%   $251.7773   $251.78   $251.80   $251.80  
  Purchase #6 $226.63   3.626%   $234.8476   $234.85   $234.85   $234.80  
  Purchase #7 $5.40   8.662%   $5.8677   $5.87   $5.85   $5.90  
  7 purchase totals = $925.54       $996.8097   $996.82   $996.80   $996.90