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 $68.62   6.264%   $72.9184   $72.92   $72.90   $72.90  
  Purchase #2 $51.61   7.220%   $55.3362   $55.34   $55.35   $55.30  
  Purchase #3 $103.51   13.192%   $117.165   $117.17   $117.15   $117.20  
  Purchase #4 $151.77   11.335%   $168.9731   $168.97   $168.95   $169.00  
  Purchase #5 $212.34   7.106%   $227.4289   $227.43   $227.45   $227.40  
  Purchase #6 $178.67   13.394%   $202.6011   $202.60   $202.60   $202.60  
  Purchase #7 $142.26   10.242%   $156.8303   $156.83   $156.85   $156.80  
  7 purchase totals = $908.78       $1,001.2530   $1,001.26   $1,001.25   $1,001.20