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	$105.65	13.724%	$120.1494	$120.15	$120.15	$120.10
Purchase #2	$10.85	12.581%	$12.215	$12.22	$12.20	$12.20
Purchase #3	$213.82	3.572%	$221.4577	$221.46	$221.45	$221.50
Purchase #4	$217.81	9.662%	$238.8548	$238.85	$238.85	$238.90
Purchase #5	$93.98	12.286%	$105.5264	$105.53	$105.55	$105.50
Purchase #6	$99.87	12.310%	$112.164	$112.16	$112.15	$112.20
Purchase #7	$79.76	3.751%	$82.7518	$82.75	$82.75	$82.80
7 purchase totals =	$821.74		$893.1191	$893.12	$893.10	$893.20