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	$70.56	5.782%	$74.6398	$74.64	$74.65	$74.60
Purchase #2	$50.82	9.429%	$55.6118	$55.61	$55.60	$55.60
Purchase #3	$140.60	7.544%	$151.2069	$151.21	$151.20	$151.20
Purchase #4	$65.65	9.462%	$71.8618	$71.86	$71.85	$71.90
Purchase #5	$98.25	13.362%	$111.3782	$111.38	$111.40	$111.40
Purchase #6	$5.57	13.409%	$6.3169	$6.32	$6.30	$6.30
Purchase #7	$94.29	10.206%	$103.9132	$103.91	$103.90	$103.90
7 purchase totals =	$525.74		$574.9286	$574.93	$574.90	$574.90