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 $203.82   3.531%   $211.0169   $211.02   $211.00   $211.00  
  Purchase #2 $21.29   10.540%   $23.534   $23.53   $23.55   $23.50  
  Purchase #3 $244.45   9.298%   $267.179   $267.18   $267.20   $267.20  
  Purchase #4 $87.59   7.327%   $94.0077   $94.01   $94.00   $94.00  
  Purchase #5 $124.61   8.292%   $134.9427   $134.94   $134.95   $134.90  
  Purchase #6 $30.95   4.267%   $32.2706   $32.27   $32.25   $32.30  
  Purchase #7 $10.91   7.516%   $11.73   $11.73   $11.75   $11.70  
  7 purchase totals = $723.62       $774.6809   $774.68   $774.70   $774.60