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	$130.96	6.638%	$139.6531	$139.65	$139.65	$139.70
Purchase #2	$200.36	10.568%	$221.534	$221.53	$221.55	$221.50
Purchase #3	$166.49	3.508%	$172.3305	$172.33	$172.35	$172.30
Purchase #4	$51.73	4.128%	$53.8654	$53.87	$53.85	$53.90
Purchase #5	$85.76	4.440%	$89.5677	$89.57	$89.55	$89.60
Purchase #6	$215.28	13.309%	$243.9316	$243.93	$243.95	$243.90
Purchase #7	$61.30	6.739%	$65.431	$65.43	$65.45	$65.40
7 purchase totals =	$911.88		$986.3133	$986.31	$986.35	$986.30