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	$244.60	11.629%	$273.0445	$273.04	$273.05	$273.00
Purchase #2	$26.46	7.779%	$28.5183	$28.52	$28.50	$28.50
Purchase #3	$18.32	6.398%	$19.4921	$19.49	$19.50	$19.50
Purchase #4	$48.61	11.205%	$54.0568	$54.06	$54.05	$54.10
Purchase #5	$215.32	11.861%	$240.8591	$240.86	$240.85	$240.90
Purchase #6	$120.64	3.218%	$124.5222	$124.52	$124.50	$124.50
Purchase #7	$210.86	8.799%	$229.4136	$229.41	$229.40	$229.40
7 purchase totals =	$884.81		$969.9066	$969.90	$969.85	$969.90