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	$88.87	11.558%	$99.1416	$99.14	$99.15	$99.10
Purchase #2	$220.59	10.324%	$243.3637	$243.36	$243.35	$243.40
Purchase #3	$188.29	8.204%	$203.7373	$203.74	$203.75	$203.70
Purchase #4	$100.81	10.181%	$111.0735	$111.07	$111.05	$111.10
Purchase #5	$203.75	4.453%	$212.823	$212.82	$212.80	$212.80
Purchase #6	$59.83	5.470%	$63.1027	$63.10	$63.10	$63.10
Purchase #7	$145.81	7.310%	$156.4687	$156.47	$156.45	$156.50
7 purchase totals =	$1,007.95		$1,089.7105	$1,089.70	$1,089.65	$1,089.70