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 $70.37   5.257%   $74.0694   $74.07   $74.05   $74.10  
  Purchase #2 $56.87   5.548%   $60.0251   $60.03   $60.05   $60.00  
  Purchase #3 $206.64   3.218%   $213.2897   $213.29   $213.30   $213.30  
  Purchase #4 $176.84   9.404%   $193.47   $193.47   $193.45   $193.50  
  Purchase #5 $126.68   6.152%   $134.4734   $134.47   $134.45   $134.50  
  Purchase #6 $154.74   8.745%   $168.272   $168.27   $168.25   $168.30  
  Purchase #7 $112.58   9.781%   $123.5914   $123.59   $123.60   $123.60  
  7 purchase totals = $904.72       $967.1910   $967.19   $967.15   $967.30