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	$78.89	5.839%	$83.4964	$83.50	$83.50	$83.50
Purchase #2	$185.87	5.863%	$196.7676	$196.77	$196.75	$196.80
Purchase #3	$105.66	12.156%	$118.504	$118.50	$118.50	$118.50
Purchase #4	$156.55	5.422%	$165.0381	$165.04	$165.05	$165.00
Purchase #5	$96.30	11.449%	$107.3254	$107.33	$107.35	$107.30
Purchase #6	$30.46	9.206%	$33.2641	$33.26	$33.25	$33.30
Purchase #7	$99.67	4.666%	$104.3206	$104.32	$104.30	$104.30
7 purchase totals =	$753.40		$808.7162	$808.72	$808.70	$808.70