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	$89.40	11.715%	$99.8732	$99.87	$99.85	$99.90
Purchase #2	$214.43	3.506%	$221.9479	$221.95	$221.95	$221.90
Purchase #3	$150.46	10.528%	$166.3004	$166.30	$166.30	$166.30
Purchase #4	$122.68	12.716%	$138.28	$138.28	$138.30	$138.30
Purchase #5	$184.80	3.479%	$191.2292	$191.23	$191.25	$191.20
Purchase #6	$37.41	8.608%	$40.6303	$40.63	$40.65	$40.60
Purchase #7	$185.27	10.314%	$204.3787	$204.38	$204.40	$204.40
7 purchase totals =	$984.45		$1,062.6397	$1,062.64	$1,062.70	$1,062.60