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	$92.99	12.410%	$104.5301	$104.53	$104.55	$104.50
Purchase #2	$78.68	8.394%	$85.2844	$85.28	$85.30	$85.30
Purchase #3	$96.51	3.687%	$100.0683	$100.07	$100.05	$100.10
Purchase #4	$29.41	4.358%	$30.6917	$30.69	$30.70	$30.70
Purchase #5	$178.85	10.709%	$198.003	$198.00	$198.00	$198.00
Purchase #6	$85.38	7.851%	$92.0832	$92.08	$92.10	$92.10
Purchase #7	$35.73	4.194%	$37.2285	$37.23	$37.25	$37.20
7 purchase totals =	$597.55		$647.8892	$647.88	$647.95	$647.90