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	$198.76	12.226%	$223.0604	$223.06	$223.05	$223.10
Purchase #2	$141.49	3.252%	$146.0913	$146.09	$146.10	$146.10
Purchase #3	$210.56	5.603%	$222.3577	$222.36	$222.35	$222.40
Purchase #4	$114.33	4.838%	$119.8613	$119.86	$119.85	$119.90
Purchase #5	$80.71	12.164%	$90.5276	$90.53	$90.55	$90.50
Purchase #6	$122.82	9.155%	$134.0642	$134.06	$134.05	$134.10
Purchase #7	$246.25	12.251%	$276.4181	$276.42	$276.40	$276.40
7 purchase totals =	$1,114.92		$1,212.3806	$1,212.38	$1,212.35	$1,212.50