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 $24.67   5.665%   $26.0676   $26.07   $26.05   $26.10  
  Purchase #2 $178.99   7.151%   $191.7896   $191.79   $191.80   $191.80  
  Purchase #3 $54.90   9.566%   $60.1517   $60.15   $60.15   $60.20  
  Purchase #4 $48.87   10.152%   $53.8313   $53.83   $53.85   $53.80  
  Purchase #5 $30.52   11.416%   $34.0042   $34.00   $34.00   $34.00  
  Purchase #6 $250.86   10.798%   $277.9479   $277.95   $277.95   $277.90  
  Purchase #7 $143.85   10.817%   $159.4103   $159.41   $159.40   $159.40  
  7 purchase totals = $732.66       $803.2026   $803.20   $803.20   $803.20