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	$244.66	3.504%	$253.2329	$253.23	$253.25	$253.20
Purchase #2	$47.88	11.220%	$53.2521	$53.25	$53.25	$53.30
Purchase #3	$28.55	3.477%	$29.5427	$29.54	$29.55	$29.50
Purchase #4	$144.84	4.154%	$150.8567	$150.86	$150.85	$150.90
Purchase #5	$245.99	13.644%	$279.5529	$279.55	$279.55	$279.60
Purchase #6	$53.49	8.317%	$57.9388	$57.94	$57.95	$57.90
Purchase #7	$84.84	6.298%	$90.1832	$90.18	$90.20	$90.20
7 purchase totals =	$850.25		$914.5593	$914.55	$914.60	$914.60