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	$179.59	13.231%	$203.3516	$203.35	$203.35	$203.40
Purchase #2	$144.51	5.717%	$152.7716	$152.77	$152.75	$152.80
Purchase #3	$62.63	7.212%	$67.1469	$67.15	$67.15	$67.10
Purchase #4	$100.31	11.651%	$111.9971	$112.00	$112.00	$112.00
Purchase #5	$67.70	7.424%	$72.726	$72.73	$72.75	$72.70
Purchase #6	$160.66	10.739%	$177.9133	$177.91	$177.90	$177.90
Purchase #7	$31.92	12.353%	$35.8631	$35.86	$35.85	$35.90
7 purchase totals =	$747.32		$821.7696	$821.77	$821.75	$821.80