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	$13.55	10.750%	$15.0066	$15.01	$15.00	$15.00
Purchase #2	$83.39	8.834%	$90.7567	$90.76	$90.75	$90.80
Purchase #3	$202.72	3.118%	$209.0408	$209.04	$209.05	$209.00
Purchase #4	$198.54	10.521%	$219.4284	$219.43	$219.45	$219.40
Purchase #5	$141.62	10.765%	$156.8654	$156.87	$156.85	$156.90
Purchase #6	$140.54	4.217%	$146.4666	$146.47	$146.45	$146.50
Purchase #7	$127.56	6.846%	$136.2928	$136.29	$136.30	$136.30
7 purchase totals =	$907.92		$973.8573	$973.87	$973.85	$973.90