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	$105.80	13.137%	$119.6989	$119.70	$119.70	$119.70
Purchase #2	$72.74	8.493%	$78.9178	$78.92	$78.90	$78.90
Purchase #3	$45.61	11.201%	$50.7188	$50.72	$50.70	$50.70
Purchase #4	$172.84	10.822%	$191.5447	$191.54	$191.55	$191.50
Purchase #5	$243.37	6.294%	$258.6877	$258.69	$258.70	$258.70
Purchase #6	$34.67	8.327%	$37.557	$37.56	$37.55	$37.60
Purchase #7	$76.51	10.346%	$84.4257	$84.43	$84.45	$84.40
7 purchase totals =	$751.54		$821.5506	$821.56	$821.55	$821.50