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 $114.53   4.596%   $119.7938   $119.79   $119.80   $119.80  
  Purchase #2 $196.63   11.232%   $218.7155   $218.72   $218.70   $218.70  
  Purchase #3 $214.65   11.565%   $239.4743   $239.47   $239.45   $239.50  
  Purchase #4 $59.72   10.436%   $65.9524   $65.95   $65.95   $66.00  
  Purchase #5 $50.33   11.512%   $56.124   $56.12   $56.10   $56.10  
  Purchase #6 $237.38   12.164%   $266.2549   $266.25   $266.25   $266.30  
  Purchase #7 $150.91   12.319%   $169.5006   $169.50   $169.50   $169.50  
  7 purchase totals = $1,024.15       $1,135.8155   $1,135.80   $1,135.75   $1,135.90