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	$104.92	10.175%	$115.5956	$115.60	$115.60	$115.60
Purchase #2	$98.31	5.246%	$103.4673	$103.47	$103.45	$103.50
Purchase #3	$185.75	6.349%	$197.5433	$197.54	$197.55	$197.50
Purchase #4	$92.73	11.428%	$103.3272	$103.33	$103.35	$103.30
Purchase #5	$30.34	3.527%	$31.4101	$31.41	$31.40	$31.40
Purchase #6	$86.54	11.140%	$96.1806	$96.18	$96.20	$96.20
Purchase #7	$91.92	9.559%	$100.7066	$100.71	$100.70	$100.70
7 purchase totals =	$690.51		$748.2307	$748.24	$748.25	$748.20