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	$229.75	3.793%	$238.4644	$238.46	$238.45	$238.50
Purchase #2	$137.98	6.399%	$146.8093	$146.81	$146.80	$146.80
Purchase #3	$106.77	4.148%	$111.1988	$111.20	$111.20	$111.20
Purchase #4	$99.48	13.138%	$112.5497	$112.55	$112.55	$112.50
Purchase #5	$126.57	11.766%	$141.4622	$141.46	$141.45	$141.50
Purchase #6	$104.30	11.706%	$116.5094	$116.51	$116.50	$116.50
Purchase #7	$223.94	3.559%	$231.91	$231.91	$231.90	$231.90
7 purchase totals =	$1,028.79		$1,098.9038	$1,098.90	$1,098.85	$1,098.90