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	$75.33	9.130%	$82.2076	$82.21	$82.20	$82.20
Purchase #2	$85.63	12.718%	$96.5204	$96.52	$96.50	$96.50
Purchase #3	$146.28	12.778%	$164.9717	$164.97	$164.95	$165.00
Purchase #4	$38.30	9.811%	$42.0576	$42.06	$42.05	$42.10
Purchase #5	$122.31	13.300%	$138.5772	$138.58	$138.60	$138.60
Purchase #6	$46.63	10.302%	$51.4338	$51.43	$51.45	$51.40
Purchase #7	$28.47	11.170%	$31.6501	$31.65	$31.65	$31.70
7 purchase totals =	$542.95		$607.4184	$607.42	$607.40	$607.50