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 $165.71   12.757%   $186.8496   $186.85   $186.85   $186.80  
  Purchase #2 $232.64   6.466%   $247.6825   $247.68   $247.70   $247.70  
  Purchase #3 $49.96   13.420%   $56.6646   $56.66   $56.65   $56.70  
  Purchase #4 $97.94   4.648%   $102.4923   $102.49   $102.50   $102.50  
  Purchase #5 $248.27   11.672%   $277.2481   $277.25   $277.25   $277.20  
  Purchase #6 $45.68   10.286%   $50.3786   $50.38   $50.40   $50.40  
  Purchase #7 $9.91   11.713%   $11.0708   $11.07   $11.05   $11.10  
  7 purchase totals = $850.11       $932.3865   $932.38   $932.40   $932.40