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 $118.59   6.176%   $125.9141   $125.91   $125.90   $125.90  
  Purchase #2 $47.87   11.453%   $53.3526   $53.35   $53.35   $53.40  
  Purchase #3 $195.36   4.159%   $203.485   $203.49   $203.50   $203.50  
  Purchase #4 $75.61   9.121%   $82.5064   $82.51   $82.50   $82.50  
  Purchase #5 $13.77   6.695%   $14.6919   $14.69   $14.70   $14.70  
  Purchase #6 $16.44   6.837%   $17.564   $17.56   $17.55   $17.60  
  Purchase #7 $167.89   6.579%   $178.9355   $178.94   $178.95   $178.90  
  7 purchase totals = $635.53       $676.4495   $676.45   $676.45   $676.50