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 $68.46   5.138%   $71.9775   $71.98   $72.00   $72.00  
  Purchase #2 $41.57   10.621%   $45.9851   $45.99   $46.00   $46.00  
  Purchase #3 $73.42   10.543%   $81.1607   $81.16   $81.15   $81.20  
  Purchase #4 $211.69   3.853%   $219.8464   $219.85   $219.85   $219.80  
  Purchase #5 $90.32   6.693%   $96.3651   $96.37   $96.35   $96.40  
  Purchase #6 $200.88   12.262%   $225.5119   $225.51   $225.50   $225.50  
  Purchase #7 $97.38   13.852%   $110.8691   $110.87   $110.85   $110.90  
  7 purchase totals = $783.72       $851.7158   $851.73   $851.70   $851.80