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	$146.47	12.165%	$164.2881	$164.29	$164.30	$164.30
Purchase #2	$61.78	9.797%	$67.8326	$67.83	$67.85	$67.80
Purchase #3	$229.89	11.182%	$255.5963	$255.60	$255.60	$255.60
Purchase #4	$29.65	9.104%	$32.3493	$32.35	$32.35	$32.30
Purchase #5	$80.44	6.517%	$85.6823	$85.68	$85.70	$85.70
Purchase #6	$186.27	12.506%	$209.5649	$209.56	$209.55	$209.60
Purchase #7	$226.72	6.180%	$240.7313	$240.73	$240.75	$240.70
7 purchase totals =	$961.22		$1,056.0448	$1,056.04	$1,056.10	$1,056.00