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 $186.90   11.767%   $208.8925   $208.89   $208.90   $208.90  
  Purchase #2 $245.29   3.416%   $253.6691   $253.67   $253.65   $253.70  
  Purchase #3 $237.86   3.292%   $245.6904   $245.69   $245.70   $245.70  
  Purchase #4 $87.28   6.594%   $93.0352   $93.04   $93.05   $93.00  
  Purchase #5 $221.51   8.697%   $240.7747   $240.77   $240.75   $240.80  
  Purchase #6 $107.48   7.401%   $115.4346   $115.43   $115.45   $115.40  
  Purchase #7 $107.87   10.311%   $118.9925   $118.99   $119.00   $119.00  
  7 purchase totals = $1,194.19       $1,276.4890   $1,276.48   $1,276.50   $1,276.50