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	$174.48	6.366%	$185.5874	$185.59	$185.60	$185.60
Purchase #2	$144.27	10.740%	$159.7646	$159.76	$159.75	$159.80
Purchase #3	$25.35	6.657%	$27.0375	$27.04	$27.05	$27.00
Purchase #4	$187.81	5.674%	$198.4663	$198.47	$198.45	$198.50
Purchase #5	$30.88	5.124%	$32.4623	$32.46	$32.45	$32.50
Purchase #6	$16.52	3.716%	$17.1339	$17.13	$17.15	$17.10
Purchase #7	$173.34	3.849%	$180.0119	$180.01	$180.00	$180.00
7 purchase totals =	$752.65		$800.4639	$800.46	$800.45	$800.50