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	$159.49	12.763%	$179.8457	$179.85	$179.85	$179.80
Purchase #2	$81.66	9.842%	$89.697	$89.70	$89.70	$89.70
Purchase #3	$224.96	10.473%	$248.5201	$248.52	$248.50	$248.50
Purchase #4	$25.33	11.552%	$28.2561	$28.26	$28.25	$28.30
Purchase #5	$76.77	5.652%	$81.109	$81.11	$81.10	$81.10
Purchase #6	$35.32	12.668%	$39.7943	$39.79	$39.80	$39.80
Purchase #7	$172.62	3.872%	$179.3038	$179.30	$179.30	$179.30
7 purchase totals =	$776.15		$846.5260	$846.53	$846.50	$846.50