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	$21.82	10.248%	$24.0561	$24.06	$24.05	$24.10
Purchase #2	$62.34	6.400%	$66.3298	$66.33	$66.35	$66.30
Purchase #3	$87.92	5.700%	$92.9314	$92.93	$92.95	$92.90
Purchase #4	$162.63	10.654%	$179.9566	$179.96	$179.95	$180.00
Purchase #5	$55.30	7.585%	$59.4945	$59.49	$59.50	$59.50
Purchase #6	$57.48	5.168%	$60.4506	$60.45	$60.45	$60.50
Purchase #7	$95.62	5.148%	$100.5425	$100.54	$100.55	$100.50
7 purchase totals =	$543.11		$583.7615	$583.76	$583.80	$583.80