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	$5.72	13.468%	$6.4904	$6.49	$6.50	$6.50
Purchase #2	$178.96	9.674%	$196.2726	$196.27	$196.25	$196.30
Purchase #3	$13.87	9.808%	$15.2304	$15.23	$15.25	$15.20
Purchase #4	$72.75	13.234%	$82.3777	$82.38	$82.40	$82.40
Purchase #5	$11.63	12.223%	$13.0515	$13.05	$13.05	$13.10
Purchase #6	$21.38	8.221%	$23.1376	$23.14	$23.15	$23.10
Purchase #7	$164.58	4.390%	$171.8051	$171.81	$171.80	$171.80
7 purchase totals =	$468.89		$508.3653	$508.37	$508.40	$508.40