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	$83.99	6.368%	$89.3385	$89.34	$89.35	$89.30
Purchase #2	$137.51	6.380%	$146.2831	$146.28	$146.30	$146.30
Purchase #3	$186.40	9.313%	$203.7594	$203.76	$203.75	$203.80
Purchase #4	$99.84	5.569%	$105.4001	$105.40	$105.40	$105.40
Purchase #5	$230.34	8.706%	$250.3934	$250.39	$250.40	$250.40
Purchase #6	$78.55	13.324%	$89.016	$89.02	$89.00	$89.00
Purchase #7	$105.80	6.353%	$112.5215	$112.52	$112.50	$112.50
7 purchase totals =	$922.43		$996.7120	$996.71	$996.70	$996.70