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 $82.55   11.482%   $92.0284   $92.03   $92.05   $92.00  
  Purchase #2 $153.61   5.606%   $162.2214   $162.22   $162.20   $162.20  
  Purchase #3 $99.76   13.752%   $113.479   $113.48   $113.50   $113.50  
  Purchase #4 $179.46   4.406%   $187.367   $187.37   $187.35   $187.40  
  Purchase #5 $98.88   10.400%   $109.1635   $109.16   $109.15   $109.20  
  Purchase #6 $23.88   6.302%   $25.3849   $25.38   $25.40   $25.40  
  Purchase #7 $8.39   13.360%   $9.5109   $9.51   $9.50   $9.50  
  7 purchase totals = $646.53       $699.1551   $699.15   $699.15   $699.20