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 $243.44   10.733%   $269.5684   $269.57   $269.55   $269.60  
  Purchase #2 $14.91   7.449%   $16.0206   $16.02   $16.00   $16.00  
  Purchase #3 $201.85   5.842%   $213.6421   $213.64   $213.65   $213.60  
  Purchase #4 $84.55   7.644%   $91.013   $91.01   $91.00   $91.00  
  Purchase #5 $131.34   9.854%   $144.2822   $144.28   $144.30   $144.30  
  Purchase #6 $36.87   11.520%   $41.1174   $41.12   $41.10   $41.10  
  Purchase #7 $174.49   6.239%   $185.3764   $185.38   $185.40   $185.40  
  7 purchase totals = $887.45       $961.0201   $961.02   $961.00   $961.00