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	$123.57	11.197%	$137.4061	$137.41	$137.40	$137.40
Purchase #2	$74.68	10.269%	$82.3489	$82.35	$82.35	$82.30
Purchase #3	$137.88	4.262%	$143.7564	$143.76	$143.75	$143.80
Purchase #4	$31.95	5.820%	$33.8095	$33.81	$33.80	$33.80
Purchase #5	$234.99	6.654%	$250.6262	$250.63	$250.65	$250.60
Purchase #6	$32.40	6.408%	$34.4762	$34.48	$34.50	$34.50
Purchase #7	$157.42	5.764%	$166.4937	$166.49	$166.50	$166.50
7 purchase totals =	$792.89		$848.9170	$848.93	$848.95	$848.90