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	$7.41	4.843%	$7.7689	$7.77	$7.75	$7.80
Purchase #2	$90.94	9.723%	$99.7821	$99.78	$99.80	$99.80
Purchase #3	$22.72	7.349%	$24.3897	$24.39	$24.40	$24.40
Purchase #4	$168.99	5.615%	$178.4788	$178.48	$178.50	$178.50
Purchase #5	$200.37	9.431%	$219.2669	$219.27	$219.25	$219.30
Purchase #6	$55.76	7.517%	$59.9515	$59.95	$59.95	$60.00
Purchase #7	$25.51	8.223%	$27.6077	$27.61	$27.60	$27.60
7 purchase totals =	$571.70		$617.2456	$617.25	$617.25	$617.40