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 $101.49   3.611%   $105.1548   $105.15   $105.15   $105.20  
  Purchase #2 $240.76   9.321%   $263.2012   $263.20   $263.20   $263.20  
  Purchase #3 $26.74   4.446%   $27.9289   $27.93   $27.95   $27.90  
  Purchase #4 $97.98   9.172%   $106.9667   $106.97   $106.95   $107.00  
  Purchase #5 $182.29   6.194%   $193.581   $193.58   $193.60   $193.60  
  Purchase #6 $42.31   6.471%   $45.0479   $45.05   $45.05   $45.00  
  Purchase #7 $72.51   6.178%   $76.9897   $76.99   $77.00   $77.00  
  7 purchase totals = $764.08       $818.8702   $818.87   $818.90   $818.90