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	$73.88	6.441%	$78.6386	$78.64	$78.65	$78.60
Purchase #2	$71.61	4.408%	$74.7666	$74.77	$74.75	$74.80
Purchase #3	$38.45	8.116%	$41.5706	$41.57	$41.55	$41.60
Purchase #4	$224.41	10.620%	$248.2423	$248.24	$248.25	$248.20
Purchase #5	$139.86	4.662%	$146.3803	$146.38	$146.40	$146.40
Purchase #6	$249.39	8.750%	$271.2116	$271.21	$271.20	$271.20
Purchase #7	$133.70	6.303%	$142.1271	$142.13	$142.15	$142.10
7 purchase totals =	$931.30		$1,002.9371	$1,002.94	$1,002.95	$1,002.90