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 $32.95   4.766%   $34.5204   $34.52   $34.50   $34.50  
  Purchase #2 $213.93   13.289%   $242.3592   $242.36   $242.35   $242.40  
  Purchase #3 $37.99   5.585%   $40.1117   $40.11   $40.10   $40.10  
  Purchase #4 $10.90   13.419%   $12.3627   $12.36   $12.35   $12.40  
  Purchase #5 $12.82   13.452%   $14.5445   $14.54   $14.55   $14.50  
  Purchase #6 $224.98   7.250%   $241.2911   $241.29   $241.30   $241.30  
  Purchase #7 $249.64   12.483%   $280.8026   $280.80   $280.80   $280.80  
  7 purchase totals = $783.21       $865.9922   $865.98   $865.95   $866.00