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	$218.36	11.251%	$242.9277	$242.93	$242.95	$242.90
Purchase #2	$137.87	9.147%	$150.481	$150.48	$150.50	$150.50
Purchase #3	$69.88	9.773%	$76.7094	$76.71	$76.70	$76.70
Purchase #4	$95.61	4.405%	$99.8216	$99.82	$99.80	$99.80
Purchase #5	$138.54	5.549%	$146.2276	$146.23	$146.25	$146.20
Purchase #6	$104.92	6.537%	$111.7786	$111.78	$111.80	$111.80
Purchase #7	$42.39	7.832%	$45.71	$45.71	$45.70	$45.70
7 purchase totals =	$807.57		$873.6559	$873.66	$873.70	$873.60