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 $223.98   13.539%   $254.3047   $254.30   $254.30   $254.30  
  Purchase #2 $188.44   4.521%   $196.9594   $196.96   $196.95   $197.00  
  Purchase #3 $60.32   7.638%   $64.9272   $64.93   $64.95   $64.90  
  Purchase #4 $16.61   7.612%   $17.8744   $17.87   $17.85   $17.90  
  Purchase #5 $205.60   6.329%   $218.6124   $218.61   $218.60   $218.60  
  Purchase #6 $78.60   11.443%   $87.5942   $87.59   $87.60   $87.60  
  Purchase #7 $37.86   10.128%   $41.6945   $41.69   $41.70   $41.70  
  7 purchase totals = $811.41       $881.9668   $881.95   $881.95   $882.00