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 $213.83   6.126%   $226.9292   $226.93   $226.95   $226.90  
  Purchase #2 $120.98   8.806%   $131.6335   $131.63   $131.65   $131.60  
  Purchase #3 $232.51   9.607%   $254.8472   $254.85   $254.85   $254.80  
  Purchase #4 $61.25   8.373%   $66.3785   $66.38   $66.40   $66.40  
  Purchase #5 $196.93   13.465%   $223.4466   $223.45   $223.45   $223.40  
  Purchase #6 $239.77   7.245%   $257.1413   $257.14   $257.15   $257.10  
  Purchase #7 $231.71   9.665%   $254.1048   $254.10   $254.10   $254.10  
  7 purchase totals = $1,296.98       $1,414.4811   $1,414.48   $1,414.55   $1,414.30