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	$204.78	13.837%	$233.1154	$233.12	$233.10	$233.10
Purchase #2	$114.91	10.577%	$127.064	$127.06	$127.05	$127.10
Purchase #3	$42.62	6.337%	$45.3208	$45.32	$45.30	$45.30
Purchase #4	$158.32	8.214%	$171.3244	$171.32	$171.30	$171.30
Purchase #5	$165.91	13.779%	$188.7707	$188.77	$188.75	$188.80
Purchase #6	$81.74	9.810%	$89.7587	$89.76	$89.75	$89.80
Purchase #7	$111.78	12.324%	$125.5558	$125.56	$125.55	$125.60
7 purchase totals =	$880.06		$980.9098	$980.91	$980.80	$981.00