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	$84.48	6.424%	$89.907	$89.91	$89.90	$89.90
Purchase #2	$127.60	4.711%	$133.6112	$133.61	$133.60	$133.60
Purchase #3	$151.41	6.171%	$160.7535	$160.75	$160.75	$160.80
Purchase #4	$187.79	12.510%	$211.2825	$211.28	$211.30	$211.30
Purchase #5	$246.71	11.853%	$275.9525	$275.95	$275.95	$276.00
Purchase #6	$80.54	10.612%	$89.0869	$89.09	$89.10	$89.10
Purchase #7	$204.98	6.399%	$218.0967	$218.10	$218.10	$218.10
7 purchase totals =	$1,083.51		$1,178.6903	$1,178.69	$1,178.70	$1,178.80