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 $14.86   4.351%   $15.5066   $15.51   $15.50   $15.50  
  Purchase #2 $196.47   11.668%   $219.3941   $219.39   $219.40   $219.40  
  Purchase #3 $190.30   6.626%   $202.9093   $202.91   $202.90   $202.90  
  Purchase #4 $133.37   4.394%   $139.2303   $139.23   $139.25   $139.20  
  Purchase #5 $177.51   13.246%   $201.023   $201.02   $201.00   $201.00  
  Purchase #6 $53.46   6.377%   $56.8691   $56.87   $56.85   $56.90  
  Purchase #7 $45.70   8.555%   $49.6096   $49.61   $49.60   $49.60  
  7 purchase totals = $811.67       $884.5420   $884.54   $884.50   $884.50