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	$82.82	7.494%	$89.0265	$89.03	$89.05	$89.00
Purchase #2	$89.32	9.347%	$97.6687	$97.67	$97.65	$97.70
Purchase #3	$79.85	13.190%	$90.3822	$90.38	$90.40	$90.40
Purchase #4	$43.89	5.235%	$46.1876	$46.19	$46.20	$46.20
Purchase #5	$39.29	8.852%	$42.768	$42.77	$42.75	$42.80
Purchase #6	$186.90	11.136%	$207.7132	$207.71	$207.70	$207.70
Purchase #7	$181.83	5.411%	$191.6688	$191.67	$191.65	$191.70
7 purchase totals =	$703.90		$765.4150	$765.42	$765.40	$765.50