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	$170.33	12.282%	$191.2499	$191.25	$191.25	$191.20
Purchase #2	$114.51	7.239%	$122.7994	$122.80	$122.80	$122.80
Purchase #3	$196.59	3.667%	$203.799	$203.80	$203.80	$203.80
Purchase #4	$222.42	7.272%	$238.5944	$238.59	$238.60	$238.60
Purchase #5	$119.31	9.272%	$130.3724	$130.37	$130.35	$130.40
Purchase #6	$188.76	4.332%	$196.9371	$196.94	$196.95	$196.90
Purchase #7	$42.91	12.169%	$48.1317	$48.13	$48.15	$48.10
7 purchase totals =	$1,054.83		$1,131.8839	$1,131.88	$1,131.90	$1,131.80