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 $53.66   10.362%   $59.2202   $59.22   $59.20   $59.20  
  Purchase #2 $48.28   3.156%   $49.8037   $49.80   $49.80   $49.80  
  Purchase #3 $73.49   13.365%   $83.3119   $83.31   $83.30   $83.30  
  Purchase #4 $132.96   7.116%   $142.4214   $142.42   $142.40   $142.40  
  Purchase #5 $155.82   13.402%   $176.703   $176.70   $176.70   $176.70  
  Purchase #6 $145.56   11.528%   $162.3402   $162.34   $162.35   $162.30  
  Purchase #7 $41.93   5.490%   $44.232   $44.23   $44.25   $44.20  
  7 purchase totals = $651.70       $718.0324   $718.02   $718.00   $717.90