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	$38.74	10.547%	$42.8259	$42.83	$42.85	$42.80
Purchase #2	$98.48	5.419%	$103.8166	$103.82	$103.80	$103.80
Purchase #3	$106.34	3.549%	$110.114	$110.11	$110.10	$110.10
Purchase #4	$113.75	6.162%	$120.7593	$120.76	$120.75	$120.80
Purchase #5	$61.96	4.178%	$64.5487	$64.55	$64.55	$64.50
Purchase #6	$120.63	9.661%	$132.2841	$132.28	$132.30	$132.30
Purchase #7	$179.74	9.174%	$196.2293	$196.23	$196.25	$196.20
7 purchase totals =	$719.64		$770.5779	$770.58	$770.60	$770.50