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 $66.96   11.806%   $74.8653   $74.87   $74.85   $74.90  
  Purchase #2 $104.47   13.394%   $118.4627   $118.46   $118.45   $118.50  
  Purchase #3 $26.47   3.643%   $27.4343   $27.43   $27.45   $27.40  
  Purchase #4 $192.26   6.243%   $204.2628   $204.26   $204.25   $204.30  
  Purchase #5 $229.50   5.762%   $242.7238   $242.72   $242.70   $242.70  
  Purchase #6 $130.72   5.216%   $137.5384   $137.54   $137.55   $137.50  
  Purchase #7 $228.41   5.177%   $240.2348   $240.23   $240.25   $240.20  
  7 purchase totals = $978.79       $1,045.5221   $1,045.51   $1,045.50   $1,045.50