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	$165.27	11.547%	$184.3537	$184.35	$184.35	$184.40
Purchase #2	$245.55	3.840%	$254.9791	$254.98	$255.00	$255.00
Purchase #3	$134.31	10.244%	$148.0687	$148.07	$148.05	$148.10
Purchase #4	$64.55	11.210%	$71.7861	$71.79	$71.80	$71.80
Purchase #5	$39.74	9.233%	$43.4092	$43.41	$43.40	$43.40
Purchase #6	$132.79	8.262%	$143.7611	$143.76	$143.75	$143.80
Purchase #7	$35.31	7.741%	$38.0433	$38.04	$38.05	$38.00
7 purchase totals =	$817.52		$884.4012	$884.40	$884.40	$884.50