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	$198.82	10.558%	$219.8114	$219.81	$219.80	$219.80
Purchase #2	$178.58	5.117%	$187.7179	$187.72	$187.70	$187.70
Purchase #3	$94.28	8.500%	$102.2938	$102.29	$102.30	$102.30
Purchase #4	$218.50	5.254%	$229.98	$229.98	$230.00	$230.00
Purchase #5	$54.87	11.374%	$61.1109	$61.11	$61.10	$61.10
Purchase #6	$40.82	3.625%	$42.2997	$42.30	$42.30	$42.30
Purchase #7	$123.89	3.739%	$128.5222	$128.52	$128.50	$128.50
7 purchase totals =	$909.76		$971.7359	$971.73	$971.70	$971.70