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	$21.50	12.102%	$24.1019	$24.10	$24.10	$24.10
Purchase #2	$87.76	3.730%	$91.0334	$91.03	$91.05	$91.00
Purchase #3	$214.50	4.167%	$223.4382	$223.44	$223.45	$223.40
Purchase #4	$8.89	13.474%	$10.0878	$10.09	$10.10	$10.10
Purchase #5	$99.63	9.751%	$109.3449	$109.34	$109.35	$109.30
Purchase #6	$200.59	9.441%	$219.5277	$219.53	$219.55	$219.50
Purchase #7	$53.67	10.161%	$59.1234	$59.12	$59.10	$59.10
7 purchase totals =	$686.54		$736.6573	$736.65	$736.70	$736.50