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	$85.58	4.181%	$89.1581	$89.16	$89.15	$89.20
Purchase #2	$126.50	11.750%	$141.3638	$141.36	$141.35	$141.40
Purchase #3	$108.86	9.514%	$119.2169	$119.22	$119.20	$119.20
Purchase #4	$46.72	11.854%	$52.2582	$52.26	$52.25	$52.30
Purchase #5	$109.91	8.471%	$119.2205	$119.22	$119.20	$119.20
Purchase #6	$55.50	10.719%	$61.449	$61.45	$61.45	$61.40
Purchase #7	$178.66	13.237%	$202.3092	$202.31	$202.30	$202.30
7 purchase totals =	$711.73		$784.9757	$784.98	$784.90	$785.00