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	$70.53	3.356%	$72.897	$72.90	$72.90	$72.90
Purchase #2	$144.80	11.464%	$161.3999	$161.40	$161.40	$161.40
Purchase #3	$146.36	6.481%	$155.8456	$155.85	$155.85	$155.80
Purchase #4	$206.59	4.508%	$215.9031	$215.90	$215.90	$215.90
Purchase #5	$116.30	12.123%	$130.399	$130.40	$130.40	$130.40
Purchase #6	$56.85	13.798%	$64.6942	$64.69	$64.70	$64.70
Purchase #7	$149.62	13.235%	$169.4222	$169.42	$169.40	$169.40
7 purchase totals =	$891.05		$970.5610	$970.56	$970.55	$970.50