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 $67.73   6.792%   $72.3302   $72.33   $72.35   $72.30  
  Purchase #2 $177.90   11.705%   $198.7232   $198.72   $198.70   $198.70  
  Purchase #3 $161.26   10.222%   $177.744   $177.74   $177.75   $177.70  
  Purchase #4 $245.56   9.535%   $268.9741   $268.97   $268.95   $269.00  
  Purchase #5 $169.78   11.289%   $188.9465   $188.95   $188.95   $188.90  
  Purchase #6 $75.49   12.383%   $84.8379   $84.84   $84.85   $84.80  
  Purchase #7 $221.82   12.669%   $249.9224   $249.92   $249.90   $249.90  
  7 purchase totals = $1,119.54       $1,241.4783   $1,241.47   $1,241.45   $1,241.30