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	$27.61	3.348%	$28.5344	$28.53	$28.55	$28.50
Purchase #2	$50.86	6.454%	$54.1425	$54.14	$54.15	$54.10
Purchase #3	$247.70	13.164%	$280.3072	$280.31	$280.30	$280.30
Purchase #4	$235.81	8.133%	$254.9884	$254.99	$255.00	$255.00
Purchase #5	$87.76	13.754%	$99.8305	$99.83	$99.85	$99.80
Purchase #6	$69.71	10.608%	$77.1048	$77.10	$77.10	$77.10
Purchase #7	$229.71	13.432%	$260.5646	$260.56	$260.55	$260.60
7 purchase totals =	$949.16		$1,055.4724	$1,055.46	$1,055.50	$1,055.40