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 $61.34   12.621%   $69.0817   $69.08   $69.10   $69.10  
  Purchase #2 $122.35   10.682%   $135.4194   $135.42   $135.40   $135.40  
  Purchase #3 $230.64   3.692%   $239.1552   $239.16   $239.15   $239.20  
  Purchase #4 $161.66   8.635%   $175.6193   $175.62   $175.60   $175.60  
  Purchase #5 $197.40   4.309%   $205.906   $205.91   $205.90   $205.90  
  Purchase #6 $218.35   11.446%   $243.3423   $243.34   $243.35   $243.30  
  Purchase #7 $27.73   11.118%   $30.813   $30.81   $30.80   $30.80  
  7 purchase totals = $1,019.47       $1,099.3369   $1,099.34   $1,099.30   $1,099.30