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	$129.98	4.671%	$136.0514	$136.05	$136.05	$136.10
Purchase #2	$111.37	10.741%	$123.3323	$123.33	$123.35	$123.30
Purchase #3	$63.41	12.373%	$71.2557	$71.26	$71.25	$71.30
Purchase #4	$181.94	3.561%	$188.4189	$188.42	$188.40	$188.40
Purchase #5	$18.32	6.367%	$19.4864	$19.49	$19.50	$19.50
Purchase #6	$170.70	9.444%	$186.8209	$186.82	$186.80	$186.80
Purchase #7	$89.31	5.370%	$94.1059	$94.11	$94.10	$94.10
7 purchase totals =	$765.03		$819.4715	$819.48	$819.45	$819.50