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	$17.96	13.172%	$20.3257	$20.33	$20.35	$20.30
Purchase #2	$206.99	8.684%	$224.965	$224.97	$224.95	$225.00
Purchase #3	$248.62	7.117%	$266.3143	$266.31	$266.30	$266.30
Purchase #4	$51.31	6.845%	$54.8222	$54.82	$54.80	$54.80
Purchase #5	$230.92	8.655%	$250.9061	$250.91	$250.90	$250.90
Purchase #6	$53.54	11.549%	$59.7233	$59.72	$59.70	$59.70
Purchase #7	$102.50	13.743%	$116.5866	$116.59	$116.60	$116.60
7 purchase totals =	$911.84		$993.6432	$993.65	$993.60	$993.60