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	$159.82	7.379%	$171.6131	$171.61	$171.60	$171.60
Purchase #2	$224.99	11.255%	$250.3126	$250.31	$250.30	$250.30
Purchase #3	$243.49	13.322%	$275.9277	$275.93	$275.95	$275.90
Purchase #4	$249.62	7.527%	$268.4089	$268.41	$268.40	$268.40
Purchase #5	$65.50	9.172%	$71.5077	$71.51	$71.50	$71.50
Purchase #6	$135.45	11.845%	$151.4941	$151.49	$151.50	$151.50
Purchase #7	$250.32	12.770%	$282.2859	$282.29	$282.30	$282.30
7 purchase totals =	$1,329.19		$1,471.5500	$1,471.55	$1,471.55	$1,471.50