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	$30.38	3.297%	$31.3816	$31.38	$31.40	$31.40
Purchase #2	$242.31	6.589%	$258.2758	$258.28	$258.30	$258.30
Purchase #3	$83.55	6.726%	$89.1696	$89.17	$89.15	$89.20
Purchase #4	$178.94	9.826%	$196.5226	$196.52	$196.50	$196.50
Purchase #5	$109.80	4.613%	$114.8651	$114.87	$114.85	$114.90
Purchase #6	$228.36	10.290%	$251.8582	$251.86	$251.85	$251.90
Purchase #7	$69.44	13.113%	$78.5457	$78.55	$78.55	$78.50
7 purchase totals =	$942.78		$1,020.6186	$1,020.63	$1,020.60	$1,020.70