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 $45.77   10.248%   $50.4605   $50.46   $50.45   $50.50  
  Purchase #2 $79.67   5.806%   $84.2956   $84.30   $84.30   $84.30  
  Purchase #3 $91.69   7.242%   $98.3302   $98.33   $98.35   $98.30  
  Purchase #4 $240.93   7.872%   $259.896   $259.90   $259.90   $259.90  
  Purchase #5 $97.76   4.354%   $102.0165   $102.02   $102.00   $102.00  
  Purchase #6 $189.87   13.454%   $215.4151   $215.42   $215.40   $215.40  
  Purchase #7 $208.51   12.461%   $234.4924   $234.49   $234.50   $234.50  
  7 purchase totals = $954.20       $1,044.9063   $1,044.92   $1,044.90   $1,044.90