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	$123.98	8.627%	$134.6758	$134.68	$134.70	$134.70
Purchase #2	$15.34	3.790%	$15.9214	$15.92	$15.90	$15.90
Purchase #3	$10.86	3.643%	$11.2556	$11.26	$11.25	$11.30
Purchase #4	$31.50	7.642%	$33.9072	$33.91	$33.90	$33.90
Purchase #5	$98.86	3.589%	$102.4081	$102.41	$102.40	$102.40
Purchase #6	$86.50	11.713%	$96.6317	$96.63	$96.65	$96.60
Purchase #7	$40.48	5.181%	$42.5773	$42.58	$42.60	$42.60
7 purchase totals =	$407.52		$437.3771	$437.39	$437.40	$437.40