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 $223.63   9.535%   $244.9531   $244.95   $244.95   $245.00  
  Purchase #2 $183.36   10.507%   $202.6256   $202.63   $202.65   $202.60  
  Purchase #3 $37.78   8.550%   $41.0102   $41.01   $41.00   $41.00  
  Purchase #4 $32.67   3.326%   $33.7566   $33.76   $33.75   $33.80  
  Purchase #5 $90.78   13.479%   $103.0162   $103.02   $103.00   $103.00  
  Purchase #6 $18.30   3.551%   $18.9498   $18.95   $18.95   $18.90  
  Purchase #7 $14.32   3.156%   $14.7719   $14.77   $14.75   $14.80  
  7 purchase totals = $600.84       $659.0834   $659.09   $659.05   $659.10