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 $73.87   4.801%   $77.4165   $77.42   $77.40   $77.40  
  Purchase #2 $87.53   9.606%   $95.9381   $95.94   $95.95   $95.90  
  Purchase #3 $181.87   7.562%   $195.623   $195.62   $195.60   $195.60  
  Purchase #4 $107.28   7.769%   $115.6146   $115.61   $115.60   $115.60  
  Purchase #5 $113.44   4.328%   $118.3497   $118.35   $118.35   $118.30  
  Purchase #6 $109.60   6.385%   $116.598   $116.60   $116.60   $116.60  
  Purchase #7 $202.75   7.598%   $218.1549   $218.15   $218.15   $218.20  
  7 purchase totals = $876.34       $937.6948   $937.69   $937.65   $937.60