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 $23.65   4.279%   $24.662   $24.66   $24.65   $24.70  
  Purchase #2 $10.30   10.230%   $11.3537   $11.35   $11.35   $11.40  
  Purchase #3 $23.76   13.631%   $26.9987   $27.00   $27.00   $27.00  
  Purchase #4 $141.66   13.693%   $161.0575   $161.06   $161.05   $161.10  
  Purchase #5 $194.55   3.336%   $201.0402   $201.04   $201.05   $201.00  
  Purchase #6 $16.72   10.469%   $18.4704   $18.47   $18.45   $18.50  
  Purchase #7 $247.70   12.610%   $278.935   $278.94   $278.95   $278.90  
  7 purchase totals = $658.34       $722.5175   $722.52   $722.50   $722.60