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	$31.68	6.337%	$33.6876	$33.69	$33.70	$33.70
Purchase #2	$178.50	5.595%	$188.4871	$188.49	$188.50	$188.50
Purchase #3	$239.44	7.452%	$257.2831	$257.28	$257.30	$257.30
Purchase #4	$50.83	4.873%	$53.3069	$53.31	$53.30	$53.30
Purchase #5	$10.46	6.430%	$11.1326	$11.13	$11.15	$11.10
Purchase #6	$184.68	6.419%	$196.5346	$196.53	$196.55	$196.50
Purchase #7	$49.33	4.558%	$51.5785	$51.58	$51.60	$51.60
7 purchase totals =	$744.92		$792.0104	$792.01	$792.10	$792.00