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 $59.65   9.359%   $65.2326   $65.23   $65.25   $65.20  
  Purchase #2 $191.92   3.574%   $198.7792   $198.78   $198.80   $198.80  
  Purchase #3 $98.76   4.640%   $103.3425   $103.34   $103.35   $103.30  
  Purchase #4 $86.82   9.514%   $95.0801   $95.08   $95.10   $95.10  
  Purchase #5 $13.71   6.748%   $14.6352   $14.64   $14.65   $14.60  
  Purchase #6 $65.95   10.751%   $73.0403   $73.04   $73.05   $73.00  
  Purchase #7 $48.26   10.571%   $53.3616   $53.36   $53.35   $53.40  
  7 purchase totals = $565.07       $603.4715   $603.47   $603.55   $603.40