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	$35.45	11.753%	$39.6164	$39.62	$39.60	$39.60
Purchase #2	$191.66	5.706%	$202.5961	$202.60	$202.60	$202.60
Purchase #3	$148.73	11.335%	$165.5885	$165.59	$165.60	$165.60
Purchase #4	$120.58	8.321%	$130.6135	$130.61	$130.60	$130.60
Purchase #5	$126.42	11.447%	$140.8913	$140.89	$140.90	$140.90
Purchase #6	$178.82	3.238%	$184.6102	$184.61	$184.60	$184.60
Purchase #7	$175.70	11.693%	$196.2446	$196.24	$196.25	$196.20
7 purchase totals =	$977.36		$1,060.1606	$1,060.16	$1,060.15	$1,060.10