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 $112.45   12.290%   $126.2701   $126.27   $126.25   $126.30  
  Purchase #2 $92.90   9.608%   $101.8258   $101.83   $101.85   $101.80  
  Purchase #3 $32.49   5.581%   $34.3033   $34.30   $34.30   $34.30  
  Purchase #4 $79.89   8.852%   $86.9619   $86.96   $86.95   $87.00  
  Purchase #5 $122.50   12.123%   $137.3507   $137.35   $137.35   $137.40  
  Purchase #6 $184.70   13.728%   $210.0556   $210.06   $210.05   $210.10  
  Purchase #7 $60.36   6.535%   $64.3045   $64.30   $64.30   $64.30  
  7 purchase totals = $685.29       $761.0719   $761.07   $761.05   $761.20