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 $58.92   9.515%   $64.5262   $64.53   $64.55   $64.50  
  Purchase #2 $164.38   6.677%   $175.3557   $175.36   $175.35   $175.40  
  Purchase #3 $114.89   13.702%   $130.6322   $130.63   $130.65   $130.60  
  Purchase #4 $54.92   4.265%   $57.2623   $57.26   $57.25   $57.30  
  Purchase #5 $163.71   9.464%   $179.2035   $179.20   $179.20   $179.20  
  Purchase #6 $172.27   7.160%   $184.6045   $184.60   $184.60   $184.60  
  Purchase #7 $135.59   8.393%   $146.9701   $146.97   $146.95   $147.00  
  7 purchase totals = $864.68       $938.5545   $938.55   $938.55   $938.60