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 $89.69   4.691%   $93.8974   $93.90   $93.90   $93.90  
  Purchase #2 $70.63   13.153%   $79.92   $79.92   $79.90   $79.90  
  Purchase #3 $191.51   13.208%   $216.8046   $216.80   $216.80   $216.80  
  Purchase #4 $95.55   10.137%   $105.2359   $105.24   $105.25   $105.20  
  Purchase #5 $85.50   11.869%   $95.648   $95.65   $95.65   $95.60  
  Purchase #6 $35.59   12.319%   $39.9743   $39.97   $39.95   $40.00  
  Purchase #7 $212.29   10.110%   $233.7525   $233.75   $233.75   $233.80  
  7 purchase totals = $780.76       $865.2327   $865.23   $865.20   $865.20