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 $119.89   11.803%   $134.0406   $134.04   $134.05   $134.00  
  Purchase #2 $181.81   10.757%   $201.3673   $201.37   $201.35   $201.40  
  Purchase #3 $40.87   6.222%   $43.4129   $43.41   $43.40   $43.40  
  Purchase #4 $96.91   10.823%   $107.3986   $107.40   $107.40   $107.40  
  Purchase #5 $157.33   6.147%   $167.0011   $167.00   $167.00   $167.00  
  Purchase #6 $182.93   7.343%   $196.3625   $196.36   $196.35   $196.40  
  Purchase #7 $77.48   7.622%   $83.3855   $83.39   $83.40   $83.40  
  7 purchase totals = $857.22       $932.9685   $932.97   $932.95   $933.00