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	$71.37	12.502%	$80.2927	$80.29	$80.30	$80.30
Purchase #2	$85.77	12.632%	$96.6045	$96.60	$96.60	$96.60
Purchase #3	$210.91	3.669%	$218.6483	$218.65	$218.65	$218.60
Purchase #4	$21.59	4.399%	$22.5397	$22.54	$22.55	$22.50
Purchase #5	$19.35	9.813%	$21.2488	$21.25	$21.25	$21.20
Purchase #6	$56.51	8.857%	$61.5151	$61.52	$61.50	$61.50
Purchase #7	$166.66	12.870%	$188.1091	$188.11	$188.10	$188.10
7 purchase totals =	$632.16		$688.9582	$688.96	$688.95	$688.80