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	$100.82	8.704%	$109.5954	$109.60	$109.60	$109.60
Purchase #2	$95.74	4.130%	$99.6941	$99.69	$99.70	$99.70
Purchase #3	$242.86	13.329%	$275.2308	$275.23	$275.25	$275.20
Purchase #4	$149.46	10.266%	$164.8036	$164.80	$164.80	$164.80
Purchase #5	$95.57	4.458%	$99.8305	$99.83	$99.85	$99.80
Purchase #6	$237.62	3.323%	$245.5161	$245.52	$245.50	$245.50
Purchase #7	$135.58	8.198%	$146.6948	$146.69	$146.70	$146.70
7 purchase totals =	$1,057.65		$1,141.3653	$1,141.36	$1,141.40	$1,141.30