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	$109.76	12.205%	$123.1562	$123.16	$123.15	$123.20
Purchase #2	$32.42	5.459%	$34.1898	$34.19	$34.20	$34.20
Purchase #3	$94.90	6.474%	$101.0438	$101.04	$101.05	$101.00
Purchase #4	$46.45	4.411%	$48.4989	$48.50	$48.50	$48.50
Purchase #5	$115.53	11.191%	$128.459	$128.46	$128.45	$128.50
Purchase #6	$229.65	11.224%	$255.4259	$255.43	$255.45	$255.40
Purchase #7	$122.53	7.819%	$132.1106	$132.11	$132.10	$132.10
7 purchase totals =	$751.24		$822.8842	$822.89	$822.90	$822.90