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	$75.99	8.762%	$82.6482	$82.65	$82.65	$82.60
Purchase #2	$67.33	8.553%	$73.0887	$73.09	$73.10	$73.10
Purchase #3	$139.25	9.109%	$151.9343	$151.93	$151.95	$151.90
Purchase #4	$139.72	4.843%	$146.4866	$146.49	$146.50	$146.50
Purchase #5	$33.70	12.135%	$37.7895	$37.79	$37.80	$37.80
Purchase #6	$199.56	11.266%	$222.0424	$222.04	$222.05	$222.00
Purchase #7	$102.70	3.539%	$106.3346	$106.33	$106.35	$106.30
7 purchase totals =	$758.25		$820.3243	$820.32	$820.40	$820.20