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	$88.36	13.451%	$100.2453	$100.25	$100.25	$100.20
Purchase #2	$173.81	3.517%	$179.9229	$179.92	$179.90	$179.90
Purchase #3	$235.57	8.207%	$254.9032	$254.90	$254.90	$254.90
Purchase #4	$102.66	11.229%	$114.1877	$114.19	$114.20	$114.20
Purchase #5	$169.26	9.653%	$185.5987	$185.60	$185.60	$185.60
Purchase #6	$56.38	3.561%	$58.3877	$58.39	$58.40	$58.40
Purchase #7	$117.97	6.599%	$125.7548	$125.75	$125.75	$125.80
7 purchase totals =	$944.01		$1,019.0003	$1,019.00	$1,019.00	$1,019.00