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 $218.80   12.503%   $246.1566   $246.16   $246.15   $246.20  
  Purchase #2 $56.93   9.208%   $62.1721   $62.17   $62.15   $62.20  
  Purchase #3 $190.47   9.582%   $208.7208   $208.72   $208.70   $208.70  
  Purchase #4 $151.34   11.773%   $169.1573   $169.16   $169.15   $169.20  
  Purchase #5 $204.71   8.230%   $221.5576   $221.56   $221.55   $221.60  
  Purchase #6 $24.26   8.699%   $26.3704   $26.37   $26.35   $26.40  
  Purchase #7 $76.65   7.338%   $82.2746   $82.27   $82.25   $82.30  
  7 purchase totals = $923.16       $1,016.4094   $1,016.41   $1,016.30   $1,016.60