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 $67.36   8.646%   $73.1839   $73.18   $73.20   $73.20  
  Purchase #2 $98.82   3.592%   $102.3696   $102.37   $102.35   $102.40  
  Purchase #3 $76.44   13.243%   $86.5629   $86.56   $86.55   $86.60  
  Purchase #4 $142.53   8.598%   $154.7847   $154.78   $154.80   $154.80  
  Purchase #5 $95.97   9.828%   $105.4019   $105.40   $105.40   $105.40  
  Purchase #6 $90.67   3.106%   $93.4862   $93.49   $93.50   $93.50  
  Purchase #7 $105.32   3.464%   $108.9683   $108.97   $108.95   $109.00  
  7 purchase totals = $677.11       $724.7575   $724.75   $724.75   $724.90