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 $57.67   9.518%   $63.159   $63.16   $63.15   $63.20  
  Purchase #2 $202.68   4.792%   $212.3924   $212.39   $212.40   $212.40  
  Purchase #3 $124.51   10.329%   $137.3706   $137.37   $137.35   $137.40  
  Purchase #4 $206.99   9.618%   $226.8983   $226.90   $226.90   $226.90  
  Purchase #5 $178.77   6.103%   $189.6803   $189.68   $189.70   $189.70  
  Purchase #6 $154.74   7.239%   $165.9416   $165.94   $165.95   $165.90  
  Purchase #7 $16.38   10.119%   $18.0375   $18.04   $18.05   $18.00  
  7 purchase totals = $941.74       $1,013.4797   $1,013.48   $1,013.50   $1,013.50