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	$74.31	12.860%	$83.8663	$83.87	$83.85	$83.90
Purchase #2	$84.64	7.229%	$90.7586	$90.76	$90.75	$90.80
Purchase #3	$66.31	7.637%	$71.3741	$71.37	$71.35	$71.40
Purchase #4	$116.72	8.771%	$126.9575	$126.96	$126.95	$127.00
Purchase #5	$123.29	4.772%	$129.1734	$129.17	$129.15	$129.20
Purchase #6	$29.80	6.831%	$31.8356	$31.84	$31.85	$31.80
Purchase #7	$106.48	10.397%	$117.5507	$117.55	$117.55	$117.60
7 purchase totals =	$601.55		$651.5162	$651.52	$651.45	$651.70