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 $46.38   8.619%   $50.3775   $50.38   $50.40   $50.40  
  Purchase #2 $146.51   13.170%   $165.8054   $165.81   $165.80   $165.80  
  Purchase #3 $45.30   4.491%   $47.3344   $47.33   $47.35   $47.30  
  Purchase #4 $23.35   10.366%   $25.7705   $25.77   $25.75   $25.80  
  Purchase #5 $86.93   9.687%   $95.3509   $95.35   $95.35   $95.40  
  Purchase #6 $226.82   8.137%   $245.2763   $245.28   $245.30   $245.30  
  Purchase #7 $42.69   8.596%   $46.3596   $46.36   $46.35   $46.40  
  7 purchase totals = $617.98       $676.2746   $676.28   $676.30   $676.40