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 $114.71   10.437%   $126.6823   $126.68   $126.70   $126.70  
  Purchase #2 $170.94   4.344%   $178.3656   $178.37   $178.35   $178.40  
  Purchase #3 $232.68   3.734%   $241.3683   $241.37   $241.35   $241.40  
  Purchase #4 $104.74   7.183%   $112.2635   $112.26   $112.25   $112.30  
  Purchase #5 $63.99   12.832%   $72.2012   $72.20   $72.20   $72.20  
  Purchase #6 $70.84   3.259%   $73.1487   $73.15   $73.15   $73.10  
  Purchase #7 $241.37   12.830%   $272.3378   $272.34   $272.35   $272.30  
  7 purchase totals = $999.27       $1,076.3674   $1,076.37   $1,076.35   $1,076.40