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	$78.77	4.736%	$82.5005	$82.50	$82.50	$82.50
Purchase #2	$136.44	13.725%	$155.1664	$155.17	$155.15	$155.20
Purchase #3	$40.56	9.835%	$44.5491	$44.55	$44.55	$44.50
Purchase #4	$104.89	6.628%	$111.8421	$111.84	$111.85	$111.80
Purchase #5	$28.70	13.649%	$32.6173	$32.62	$32.60	$32.60
Purchase #6	$73.58	12.721%	$82.9401	$82.94	$82.95	$82.90
Purchase #7	$111.56	9.617%	$122.2887	$122.29	$122.30	$122.30
7 purchase totals =	$574.50		$631.9042	$631.91	$631.90	$631.80