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	$79.40	12.308%	$89.1726	$89.17	$89.15	$89.20
Purchase #2	$37.89	6.275%	$40.2676	$40.27	$40.25	$40.30
Purchase #3	$147.35	10.175%	$162.3429	$162.34	$162.35	$162.30
Purchase #4	$108.36	4.610%	$113.3554	$113.36	$113.35	$113.40
Purchase #5	$26.36	12.394%	$29.6271	$29.63	$29.65	$29.60
Purchase #6	$18.74	8.252%	$20.2864	$20.29	$20.30	$20.30
Purchase #7	$28.50	3.852%	$29.5978	$29.60	$29.60	$29.60
7 purchase totals =	$446.60		$484.6498	$484.66	$484.65	$484.70