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 $216.68   11.471%   $241.5354   $241.54   $241.55   $241.50  
  Purchase #2 $169.68   13.125%   $191.9505   $191.95   $191.95   $192.00  
  Purchase #3 $231.74   4.387%   $241.9064   $241.91   $241.90   $241.90  
  Purchase #4 $155.72   13.709%   $177.0677   $177.07   $177.05   $177.10  
  Purchase #5 $10.36   4.696%   $10.8465   $10.85   $10.85   $10.80  
  Purchase #6 $229.25   4.313%   $239.1376   $239.14   $239.15   $239.10  
  Purchase #7 $67.86   9.785%   $74.5001   $74.50   $74.50   $74.50  
  7 purchase totals = $1,081.29       $1,176.9442   $1,176.96   $1,176.95   $1,176.90