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	$84.32	3.438%	$87.2189	$87.22	$87.20	$87.20
Purchase #2	$143.58	6.294%	$152.6169	$152.62	$152.60	$152.60
Purchase #3	$41.52	10.234%	$45.7692	$45.77	$45.75	$45.80
Purchase #4	$140.63	10.342%	$155.174	$155.17	$155.15	$155.20
Purchase #5	$85.75	6.872%	$91.6427	$91.64	$91.65	$91.60
Purchase #6	$127.92	9.619%	$140.2246	$140.22	$140.20	$140.20
Purchase #7	$89.85	12.368%	$100.9626	$100.96	$100.95	$101.00
7 purchase totals =	$713.57		$773.6089	$773.60	$773.50	$773.60