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	$96.84	9.221%	$105.7696	$105.77	$105.75	$105.80
Purchase #2	$82.50	12.457%	$92.777	$92.78	$92.80	$92.80
Purchase #3	$67.39	7.365%	$72.3533	$72.35	$72.35	$72.40
Purchase #4	$89.85	4.687%	$94.0613	$94.06	$94.05	$94.10
Purchase #5	$94.92	11.709%	$106.0342	$106.03	$106.05	$106.00
Purchase #6	$240.72	4.601%	$251.7955	$251.80	$251.80	$251.80
Purchase #7	$42.57	8.846%	$46.3357	$46.34	$46.35	$46.30
7 purchase totals =	$714.79		$769.1266	$769.13	$769.15	$769.20