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 $202.80   11.684%   $226.4952   $226.50   $226.50   $226.50  
  Purchase #2 $144.55   8.196%   $156.3973   $156.40   $156.40   $156.40  
  Purchase #3 $47.86   8.770%   $52.0573   $52.06   $52.05   $52.10  
  Purchase #4 $198.96   3.419%   $205.7624   $205.76   $205.75   $205.80  
  Purchase #5 $20.73   10.716%   $22.9514   $22.95   $22.95   $23.00  
  Purchase #6 $56.27   4.177%   $58.6204   $58.62   $58.60   $58.60  
  Purchase #7 $142.44   8.554%   $154.6243   $154.62   $154.60   $154.60  
  7 purchase totals = $813.61       $876.9083   $876.91   $876.85   $877.00