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	$63.60	9.349%	$69.546	$69.55	$69.55	$69.50
Purchase #2	$159.79	7.612%	$171.9532	$171.95	$171.95	$172.00
Purchase #3	$122.44	5.469%	$129.1362	$129.14	$129.15	$129.10
Purchase #4	$196.57	13.107%	$222.3344	$222.33	$222.35	$222.30
Purchase #5	$241.61	5.682%	$255.3383	$255.34	$255.35	$255.30
Purchase #6	$91.55	3.224%	$94.5016	$94.50	$94.50	$94.50
Purchase #7	$142.71	4.288%	$148.8294	$148.83	$148.85	$148.80
7 purchase totals =	$1,018.27		$1,091.6391	$1,091.64	$1,091.70	$1,091.50