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	$55.48	5.484%	$58.5225	$58.52	$58.50	$58.50
Purchase #2	$136.45	10.112%	$150.2478	$150.25	$150.25	$150.20
Purchase #3	$93.94	11.792%	$105.0174	$105.02	$105.00	$105.00
Purchase #4	$111.54	8.199%	$120.6852	$120.69	$120.70	$120.70
Purchase #5	$86.83	11.205%	$96.5593	$96.56	$96.55	$96.60
Purchase #6	$109.72	12.406%	$123.3319	$123.33	$123.35	$123.30
Purchase #7	$26.52	12.130%	$29.7369	$29.74	$29.75	$29.70
7 purchase totals =	$620.48		$684.1010	$684.11	$684.10	$684.00