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 $56.63   7.824%   $61.0607   $61.06   $61.05   $61.10  
  Purchase #2 $79.60   6.295%   $84.6108   $84.61   $84.60   $84.60  
  Purchase #3 $8.49   5.872%   $8.9885   $8.99   $9.00   $9.00  
  Purchase #4 $182.87   3.535%   $189.3345   $189.33   $189.35   $189.30  
  Purchase #5 $119.35   3.562%   $123.6012   $123.60   $123.60   $123.60  
  Purchase #6 $176.78   12.713%   $199.254   $199.25   $199.25   $199.30  
  Purchase #7 $233.97   4.355%   $244.1594   $244.16   $244.15   $244.20  
  7 purchase totals = $857.69       $911.0091   $911.00   $911.00   $911.10