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	$171.46	7.648%	$184.5733	$184.57	$184.55	$184.60
Purchase #2	$59.25	7.107%	$63.4609	$63.46	$63.45	$63.50
Purchase #3	$80.70	11.759%	$90.1895	$90.19	$90.20	$90.20
Purchase #4	$197.29	13.343%	$223.6144	$223.61	$223.60	$223.60
Purchase #5	$204.53	3.869%	$212.4433	$212.44	$212.45	$212.40
Purchase #6	$45.86	8.587%	$49.798	$49.80	$49.80	$49.80
Purchase #7	$159.41	3.841%	$165.5329	$165.53	$165.55	$165.50
7 purchase totals =	$918.50		$989.6123	$989.60	$989.60	$989.60