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	$115.89	6.343%	$123.2409	$123.24	$123.25	$123.20
Purchase #2	$210.91	11.526%	$235.2195	$235.22	$235.20	$235.20
Purchase #3	$34.53	13.669%	$39.2499	$39.25	$39.25	$39.20
Purchase #4	$161.53	8.677%	$175.546	$175.55	$175.55	$175.50
Purchase #5	$154.78	13.849%	$176.2155	$176.22	$176.20	$176.20
Purchase #6	$144.62	12.579%	$162.8117	$162.81	$162.80	$162.80
Purchase #7	$192.98	3.394%	$199.5297	$199.53	$199.55	$199.50
7 purchase totals =	$1,015.24		$1,111.8132	$1,111.82	$1,111.80	$1,111.60