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	$98.82	5.212%	$103.9705	$103.97	$103.95	$104.00
Purchase #2	$80.52	6.102%	$85.4333	$85.43	$85.45	$85.40
Purchase #3	$138.76	4.757%	$145.3608	$145.36	$145.35	$145.40
Purchase #4	$113.91	4.229%	$118.7273	$118.73	$118.75	$118.70
Purchase #5	$91.55	8.687%	$99.5029	$99.50	$99.50	$99.50
Purchase #6	$169.52	10.613%	$187.5112	$187.51	$187.50	$187.50
Purchase #7	$84.25	7.154%	$90.2772	$90.28	$90.30	$90.30
7 purchase totals =	$777.33		$830.7832	$830.78	$830.80	$830.80