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	$223.53	4.632%	$233.8839	$233.88	$233.90	$233.90
Purchase #2	$152.95	11.245%	$170.1492	$170.15	$170.15	$170.10
Purchase #3	$181.87	12.643%	$204.8638	$204.86	$204.85	$204.90
Purchase #4	$99.60	6.474%	$106.0481	$106.05	$106.05	$106.00
Purchase #5	$98.78	13.305%	$111.9227	$111.92	$111.90	$111.90
Purchase #6	$142.92	9.421%	$156.3845	$156.38	$156.40	$156.40
Purchase #7	$85.30	13.143%	$96.511	$96.51	$96.50	$96.50
7 purchase totals =	$984.95		$1,079.7632	$1,079.75	$1,079.75	$1,079.70