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 $190.58   9.652%   $208.9748   $208.97   $208.95   $209.00  
  Purchase #2 $41.56   6.554%   $44.2838   $44.28   $44.30   $44.30  
  Purchase #3 $178.83   3.427%   $184.9585   $184.96   $184.95   $185.00  
  Purchase #4 $218.44   5.737%   $230.9719   $230.97   $230.95   $231.00  
  Purchase #5 $243.25   11.506%   $271.2383   $271.24   $271.25   $271.20  
  Purchase #6 $193.73   6.641%   $206.5956   $206.60   $206.60   $206.60  
  Purchase #7 $112.96   4.236%   $117.745   $117.75   $117.75   $117.70  
  7 purchase totals = $1,179.35       $1,264.7679   $1,264.77   $1,264.75   $1,264.80