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 $60.37   5.566%   $63.7302   $63.73   $63.75   $63.70  
  Purchase #2 $42.29   5.535%   $44.6308   $44.63   $44.65   $44.60  
  Purchase #3 $172.87   4.239%   $180.198   $180.20   $180.20   $180.20  
  Purchase #4 $208.93   11.836%   $233.659   $233.66   $233.65   $233.70  
  Purchase #5 $45.32   8.774%   $49.2964   $49.30   $49.30   $49.30  
  Purchase #6 $144.72   9.329%   $158.2209   $158.22   $158.20   $158.20  
  Purchase #7 $42.49   6.341%   $45.1843   $45.18   $45.20   $45.20  
  7 purchase totals = $716.99       $774.9196   $774.92   $774.95   $774.90