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	$59.92	11.208%	$66.6358	$66.64	$66.65	$66.60
Purchase #2	$148.71	4.616%	$155.5745	$155.57	$155.55	$155.60
Purchase #3	$204.91	7.486%	$220.2496	$220.25	$220.25	$220.20
Purchase #4	$209.59	6.105%	$222.3855	$222.39	$222.40	$222.40
Purchase #5	$28.69	13.452%	$32.5494	$32.55	$32.55	$32.50
Purchase #6	$22.77	11.263%	$25.3346	$25.33	$25.35	$25.30
Purchase #7	$162.62	8.702%	$176.7712	$176.77	$176.75	$176.80
7 purchase totals =	$837.21		$899.5006	$899.50	$899.50	$899.40