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	$36.55	7.810%	$39.4046	$39.40	$39.40	$39.40
Purchase #2	$28.82	11.849%	$32.2349	$32.23	$32.25	$32.20
Purchase #3	$72.50	13.564%	$82.3339	$82.33	$82.35	$82.30
Purchase #4	$53.36	3.619%	$55.2911	$55.29	$55.30	$55.30
Purchase #5	$113.35	4.536%	$118.4916	$118.49	$118.50	$118.50
Purchase #6	$59.66	12.735%	$67.2577	$67.26	$67.25	$67.30
Purchase #7	$129.61	6.177%	$137.616	$137.62	$137.60	$137.60
7 purchase totals =	$493.85		$532.6298	$532.62	$532.65	$532.60