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	$38.44	6.229%	$40.8344	$40.83	$40.85	$40.80
Purchase #2	$30.52	4.611%	$31.9273	$31.93	$31.95	$31.90
Purchase #3	$40.67	8.381%	$44.0786	$44.08	$44.10	$44.10
Purchase #4	$85.89	6.562%	$91.5261	$91.53	$91.55	$91.50
Purchase #5	$104.44	6.679%	$111.4155	$111.42	$111.40	$111.40
Purchase #6	$202.30	13.399%	$229.4062	$229.41	$229.40	$229.40
Purchase #7	$122.26	13.782%	$139.1099	$139.11	$139.10	$139.10
7 purchase totals =	$624.52		$688.2980	$688.31	$688.35	$688.20