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	$231.57	12.421%	$260.3333	$260.33	$260.35	$260.30
Purchase #2	$113.71	12.476%	$127.8965	$127.90	$127.90	$127.90
Purchase #3	$127.66	7.600%	$137.3622	$137.36	$137.35	$137.40
Purchase #4	$89.85	7.780%	$96.8403	$96.84	$96.85	$96.80
Purchase #5	$134.90	8.453%	$146.3031	$146.30	$146.30	$146.30
Purchase #6	$130.83	4.530%	$136.7566	$136.76	$136.75	$136.80
Purchase #7	$105.32	9.396%	$115.2159	$115.22	$115.20	$115.20
7 purchase totals =	$933.84		$1,020.7079	$1,020.71	$1,020.70	$1,020.70