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	$158.57	12.633%	$178.6021	$178.60	$178.60	$178.60
Purchase #2	$62.33	3.487%	$64.5034	$64.50	$64.50	$64.50
Purchase #3	$242.91	8.780%	$264.2375	$264.24	$264.25	$264.20
Purchase #4	$104.90	6.820%	$112.0542	$112.05	$112.05	$112.10
Purchase #5	$59.29	3.783%	$61.5329	$61.53	$61.55	$61.50
Purchase #6	$158.29	12.816%	$178.5764	$178.58	$178.60	$178.60
Purchase #7	$100.53	10.377%	$110.962	$110.96	$110.95	$111.00
7 purchase totals =	$886.82		$970.4685	$970.46	$970.50	$970.50