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 $221.72   8.786%   $241.2003   $241.20   $241.20   $241.20  
  Purchase #2 $119.35   12.799%   $134.6256   $134.63   $134.65   $134.60  
  Purchase #3 $167.27   8.138%   $180.8824   $180.88   $180.90   $180.90  
  Purchase #4 $190.71   3.834%   $198.0218   $198.02   $198.00   $198.00  
  Purchase #5 $141.26   6.279%   $150.1297   $150.13   $150.15   $150.10  
  Purchase #6 $170.43   4.369%   $177.8761   $177.88   $177.90   $177.90  
  Purchase #7 $248.54   13.278%   $281.5411   $281.54   $281.55   $281.50  
  7 purchase totals = $1,259.28       $1,364.2770   $1,364.28   $1,364.35   $1,364.20