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	$84.71	12.535%	$95.3284	$95.33	$95.35	$95.30
Purchase #2	$165.25	4.508%	$172.6995	$172.70	$172.70	$172.70
Purchase #3	$141.62	4.854%	$148.4942	$148.49	$148.50	$148.50
Purchase #4	$118.86	8.395%	$128.8383	$128.84	$128.85	$128.80
Purchase #5	$188.40	3.423%	$194.8489	$194.85	$194.85	$194.80
Purchase #6	$25.48	9.422%	$27.8807	$27.88	$27.90	$27.90
Purchase #7	$194.91	7.487%	$209.5029	$209.50	$209.50	$209.50
7 purchase totals =	$919.23		$977.5929	$977.59	$977.65	$977.50