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	$33.96	13.150%	$38.4257	$38.43	$38.45	$38.40
Purchase #2	$53.39	8.262%	$57.8011	$57.80	$57.80	$57.80
Purchase #3	$50.44	13.271%	$57.1339	$57.13	$57.15	$57.10
Purchase #4	$137.25	8.173%	$148.4674	$148.47	$148.45	$148.50
Purchase #5	$180.33	4.401%	$188.2663	$188.27	$188.25	$188.30
Purchase #6	$231.77	9.798%	$254.4788	$254.48	$254.50	$254.50
Purchase #7	$217.72	4.192%	$226.8468	$226.85	$226.85	$226.80
7 purchase totals =	$904.86		$971.4200	$971.43	$971.45	$971.40