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 $114.77   12.403%   $129.0049   $129.00   $129.00   $129.00  
  Purchase #2 $140.31   11.496%   $156.44   $156.44   $156.45   $156.40  
  Purchase #3 $117.69   6.218%   $125.008   $125.01   $125.00   $125.00  
  Purchase #4 $43.73   13.260%   $49.5286   $49.53   $49.55   $49.50  
  Purchase #5 $210.40   9.296%   $229.9588   $229.96   $229.95   $230.00  
  Purchase #6 $180.35   8.621%   $195.898   $195.90   $195.90   $195.90  
  Purchase #7 $174.93   8.436%   $189.6871   $189.69   $189.70   $189.70  
  7 purchase totals = $982.18       $1,075.5254   $1,075.53   $1,075.55   $1,075.50