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	$144.25	11.390%	$160.6801	$160.68	$160.70	$160.70
Purchase #2	$6.71	6.415%	$7.1404	$7.14	$7.15	$7.10
Purchase #3	$113.54	13.118%	$128.4342	$128.43	$128.45	$128.40
Purchase #4	$75.87	13.263%	$85.9326	$85.93	$85.95	$85.90
Purchase #5	$134.32	4.392%	$140.2193	$140.22	$140.20	$140.20
Purchase #6	$101.69	11.202%	$113.0813	$113.08	$113.10	$113.10
Purchase #7	$181.98	8.169%	$196.8459	$196.85	$196.85	$196.80
7 purchase totals =	$758.36		$832.3338	$832.33	$832.40	$832.20