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	$84.41	5.575%	$89.1159	$89.12	$89.10	$89.10
Purchase #2	$118.31	7.188%	$126.8141	$126.81	$126.80	$126.80
Purchase #3	$127.96	11.170%	$142.2531	$142.25	$142.25	$142.30
Purchase #4	$225.43	12.380%	$253.3382	$253.34	$253.35	$253.30
Purchase #5	$72.27	7.772%	$77.8868	$77.89	$77.90	$77.90
Purchase #6	$129.92	5.477%	$137.0357	$137.04	$137.05	$137.00
Purchase #7	$128.47	10.317%	$141.7242	$141.72	$141.70	$141.70
7 purchase totals =	$886.77		$968.1680	$968.17	$968.15	$968.10