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	$126.52	13.630%	$143.7647	$143.76	$143.75	$143.80
Purchase #2	$235.95	6.140%	$250.4373	$250.44	$250.45	$250.40
Purchase #3	$235.31	6.294%	$250.1204	$250.12	$250.10	$250.10
Purchase #4	$216.37	11.835%	$241.9774	$241.98	$242.00	$242.00
Purchase #5	$150.60	12.473%	$169.3843	$169.38	$169.40	$169.40
Purchase #6	$66.50	4.497%	$69.4905	$69.49	$69.50	$69.50
Purchase #7	$89.58	7.607%	$96.3944	$96.39	$96.40	$96.40
7 purchase totals =	$1,120.83		$1,221.5690	$1,221.56	$1,221.60	$1,221.60