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 $245.96   12.359%   $276.3582   $276.36   $276.35   $276.40  
  Purchase #2 $64.76   11.488%   $72.1996   $72.20   $72.20   $72.20  
  Purchase #3 $75.34   5.730%   $79.657   $79.66   $79.65   $79.70  
  Purchase #4 $43.81   12.705%   $49.3761   $49.38   $49.40   $49.40  
  Purchase #5 $111.70   12.672%   $125.8546   $125.85   $125.85   $125.90  
  Purchase #6 $214.50   10.409%   $236.8273   $236.83   $236.85   $236.80  
  Purchase #7 $206.28   7.115%   $220.9568   $220.96   $220.95   $221.00  
  7 purchase totals = $962.35       $1,061.2296   $1,061.24   $1,061.25   $1,061.40