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	$165.32	3.123%	$170.4829	$170.48	$170.50	$170.50
Purchase #2	$58.89	7.639%	$63.3886	$63.39	$63.40	$63.40
Purchase #3	$63.29	10.828%	$70.143	$70.14	$70.15	$70.10
Purchase #4	$228.95	9.851%	$251.5039	$251.50	$251.50	$251.50
Purchase #5	$57.28	3.260%	$59.1473	$59.15	$59.15	$59.10
Purchase #6	$20.51	3.167%	$21.1596	$21.16	$21.15	$21.20
Purchase #7	$165.29	12.293%	$185.6091	$185.61	$185.60	$185.60
7 purchase totals =	$759.53		$821.4344	$821.43	$821.45	$821.40