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 $71.71   6.548%   $76.4056   $76.41   $76.40   $76.40  
  Purchase #2 $57.47   3.762%   $59.632   $59.63   $59.65   $59.60  
  Purchase #3 $137.36   9.226%   $150.0328   $150.03   $150.05   $150.00  
  Purchase #4 $85.64   6.609%   $91.2999   $91.30   $91.30   $91.30  
  Purchase #5 $199.92   10.351%   $220.6137   $220.61   $220.60   $220.60  
  Purchase #6 $116.99   8.150%   $126.5247   $126.52   $126.50   $126.50  
  Purchase #7 $38.81   7.431%   $41.694   $41.69   $41.70   $41.70  
  7 purchase totals = $707.90       $766.2027   $766.19   $766.20   $766.10