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	$56.78	5.654%	$59.9903	$59.99	$60.00	$60.00
Purchase #2	$214.25	9.339%	$234.2588	$234.26	$234.25	$234.30
Purchase #3	$57.72	3.830%	$59.9307	$59.93	$59.95	$59.90
Purchase #4	$209.86	11.787%	$234.5962	$234.60	$234.60	$234.60
Purchase #5	$86.57	4.242%	$90.2423	$90.24	$90.25	$90.20
Purchase #6	$147.62	12.217%	$165.6547	$165.65	$165.65	$165.70
Purchase #7	$65.82	7.225%	$70.5755	$70.58	$70.60	$70.60
7 purchase totals =	$838.62		$915.2485	$915.25	$915.30	$915.30