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 $61.34   13.701%   $69.7442   $69.74   $69.75   $69.70  
  Purchase #2 $93.68   5.579%   $98.9064   $98.91   $98.90   $98.90  
  Purchase #3 $43.79   5.868%   $46.3596   $46.36   $46.35   $46.40  
  Purchase #4 $195.78   7.797%   $211.045   $211.05   $211.05   $211.00  
  Purchase #5 $48.92   10.568%   $54.0899   $54.09   $54.10   $54.10  
  Purchase #6 $159.99   5.482%   $168.7607   $168.76   $168.75   $168.80  
  Purchase #7 $199.55   7.561%   $214.638   $214.64   $214.65   $214.60  
  7 purchase totals = $803.05       $863.5438   $863.55   $863.55   $863.50