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	$18.34	11.633%	$20.4735	$20.47	$20.45	$20.50
Purchase #2	$243.28	13.680%	$276.5607	$276.56	$276.55	$276.60
Purchase #3	$5.36	8.825%	$5.833	$5.83	$5.85	$5.80
Purchase #4	$74.63	5.290%	$78.5779	$78.58	$78.60	$78.60
Purchase #5	$29.40	3.742%	$30.5001	$30.50	$30.50	$30.50
Purchase #6	$91.72	10.650%	$101.4882	$101.49	$101.50	$101.50
Purchase #7	$18.78	9.670%	$20.596	$20.60	$20.60	$20.60
7 purchase totals =	$481.51		$534.0294	$534.03	$534.05	$534.10