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 $217.85   10.629%   $241.0053   $241.01   $241.00   $241.00  
  Purchase #2 $216.80   11.733%   $242.2371   $242.24   $242.25   $242.20  
  Purchase #3 $174.94   9.659%   $191.8375   $191.84   $191.85   $191.80  
  Purchase #4 $243.67   9.105%   $265.8562   $265.86   $265.85   $265.90  
  Purchase #5 $53.27   6.258%   $56.6036   $56.60   $56.60   $56.60  
  Purchase #6 $120.83   12.582%   $136.0328   $136.03   $136.05   $136.00  
  Purchase #7 $108.86   12.854%   $122.8529   $122.85   $122.85   $122.90  
  7 purchase totals = $1,136.22       $1,256.4254   $1,256.43   $1,256.45   $1,256.40