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 $243.82   13.441%   $276.5918   $276.59   $276.60   $276.60  
  Purchase #2 $212.42   13.126%   $240.3022   $240.30   $240.30   $240.30  
  Purchase #3 $57.81   4.544%   $60.4369   $60.44   $60.45   $60.40  
  Purchase #4 $199.40   9.868%   $219.0768   $219.08   $219.10   $219.10  
  Purchase #5 $249.72   9.837%   $274.285   $274.29   $274.30   $274.30  
  Purchase #6 $124.27   9.777%   $136.4199   $136.42   $136.40   $136.40  
  Purchase #7 $193.94   12.870%   $218.9001   $218.90   $218.90   $218.90  
  7 purchase totals = $1,281.38       $1,426.0127   $1,426.02   $1,426.05   $1,426.00