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	$243.61	12.433%	$273.898	$273.90	$273.90	$273.90
Purchase #2	$198.26	11.678%	$221.4128	$221.41	$221.40	$221.40
Purchase #3	$96.94	10.552%	$107.1691	$107.17	$107.15	$107.20
Purchase #4	$242.63	13.640%	$275.7247	$275.72	$275.70	$275.70
Purchase #5	$219.38	13.565%	$249.1389	$249.14	$249.15	$249.10
Purchase #6	$111.92	13.275%	$126.7774	$126.78	$126.80	$126.80
Purchase #7	$70.82	11.245%	$78.7837	$78.78	$78.80	$78.80
7 purchase totals =	$1,183.56		$1,332.9046	$1,332.90	$1,332.90	$1,332.90