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 $144.25   13.669%   $163.9675   $163.97   $163.95   $164.00  
  Purchase #2 $8.95   6.847%   $9.5628   $9.56   $9.55   $9.60  
  Purchase #3 $121.84   4.157%   $126.9049   $126.90   $126.90   $126.90  
  Purchase #4 $65.94   9.210%   $72.0131   $72.01   $72.00   $72.00  
  Purchase #5 $176.80   12.729%   $199.3049   $199.30   $199.30   $199.30  
  Purchase #6 $32.52   9.200%   $35.5118   $35.51   $35.50   $35.50  
  Purchase #7 $239.38   9.515%   $262.157   $262.16   $262.15   $262.20  
  7 purchase totals = $789.68       $869.4220   $869.41   $869.35   $869.50