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	$23.47	7.778%	$25.2955	$25.30	$25.30	$25.30
Purchase #2	$53.87	10.402%	$59.4736	$59.47	$59.45	$59.50
Purchase #3	$92.54	7.670%	$99.6378	$99.64	$99.65	$99.60
Purchase #4	$86.45	11.386%	$96.2932	$96.29	$96.30	$96.30
Purchase #5	$234.80	3.447%	$242.8936	$242.89	$242.90	$242.90
Purchase #6	$154.70	5.858%	$163.7623	$163.76	$163.75	$163.80
Purchase #7	$37.95	11.659%	$42.3746	$42.37	$42.35	$42.40
7 purchase totals =	$683.78		$729.7306	$729.72	$729.70	$729.80