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	$38.55	9.651%	$42.2705	$42.27	$42.25	$42.30
Purchase #2	$88.25	4.161%	$91.9221	$91.92	$91.90	$91.90
Purchase #3	$94.84	8.851%	$103.2343	$103.23	$103.25	$103.20
Purchase #4	$224.89	11.733%	$251.2763	$251.28	$251.30	$251.30
Purchase #5	$189.62	8.725%	$206.1643	$206.16	$206.15	$206.20
Purchase #6	$69.27	12.689%	$78.0597	$78.06	$78.05	$78.10
Purchase #7	$232.75	7.643%	$250.5391	$250.54	$250.55	$250.50
7 purchase totals =	$938.17		$1,023.4663	$1,023.46	$1,023.45	$1,023.50