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	$129.75	9.841%	$142.5187	$142.52	$142.50	$142.50
Purchase #2	$82.27	9.210%	$89.8471	$89.85	$89.85	$89.80
Purchase #3	$159.72	12.267%	$179.3129	$179.31	$179.30	$179.30
Purchase #4	$74.32	10.635%	$82.2239	$82.22	$82.20	$82.20
Purchase #5	$215.74	8.361%	$233.778	$233.78	$233.80	$233.80
Purchase #6	$185.45	5.204%	$195.1008	$195.10	$195.10	$195.10
Purchase #7	$179.58	8.312%	$194.5067	$194.51	$194.50	$194.50
7 purchase totals =	$1,026.83		$1,117.2881	$1,117.29	$1,117.25	$1,117.20