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	$30.87	3.713%	$32.0162	$32.02	$32.00	$32.00
Purchase #2	$212.93	12.376%	$239.2822	$239.28	$239.30	$239.30
Purchase #3	$209.43	6.769%	$223.6063	$223.61	$223.60	$223.60
Purchase #4	$82.56	9.338%	$90.2695	$90.27	$90.25	$90.30
Purchase #5	$228.49	9.687%	$250.6238	$250.62	$250.60	$250.60
Purchase #6	$76.43	11.810%	$85.4564	$85.46	$85.45	$85.50
Purchase #7	$227.80	3.103%	$234.8686	$234.87	$234.85	$234.90
7 purchase totals =	$1,068.51		$1,156.1230	$1,156.13	$1,156.05	$1,156.20