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 $186.50   11.324%   $207.6193   $207.62   $207.60   $207.60  
  Purchase #2 $33.95   7.868%   $36.6212   $36.62   $36.60   $36.60  
  Purchase #3 $138.95   12.206%   $155.9102   $155.91   $155.90   $155.90  
  Purchase #4 $44.94   5.408%   $47.3704   $47.37   $47.35   $47.40  
  Purchase #5 $58.34   5.139%   $61.3381   $61.34   $61.35   $61.30  
  Purchase #6 $197.87   7.529%   $212.7676   $212.77   $212.75   $212.80  
  Purchase #7 $218.89   10.264%   $241.3569   $241.36   $241.35   $241.40  
  7 purchase totals = $879.44       $962.9837   $962.99   $962.90   $963.00