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	$140.32	13.728%	$159.5831	$159.58	$159.60	$159.60
Purchase #2	$106.80	12.746%	$120.4127	$120.41	$120.40	$120.40
Purchase #3	$90.97	10.247%	$100.2917	$100.29	$100.30	$100.30
Purchase #4	$30.87	9.451%	$33.7875	$33.79	$33.80	$33.80
Purchase #5	$140.42	5.872%	$148.6655	$148.67	$148.65	$148.70
Purchase #6	$244.57	5.705%	$258.5227	$258.52	$258.50	$258.50
Purchase #7	$45.54	11.210%	$50.645	$50.65	$50.65	$50.60
7 purchase totals =	$799.49		$871.9082	$871.91	$871.90	$871.90