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	$241.71	10.610%	$267.3554	$267.36	$267.35	$267.40
Purchase #2	$54.40	4.857%	$57.0422	$57.04	$57.05	$57.00
Purchase #3	$45.97	11.611%	$51.3076	$51.31	$51.30	$51.30
Purchase #4	$72.56	13.359%	$82.2533	$82.25	$82.25	$82.30
Purchase #5	$70.28	12.402%	$78.9961	$79.00	$79.00	$79.00
Purchase #6	$166.50	12.452%	$187.2326	$187.23	$187.25	$187.20
Purchase #7	$99.28	12.312%	$111.5034	$111.50	$111.50	$111.50
7 purchase totals =	$750.70		$835.6906	$835.69	$835.70	$835.70