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	$72.90	7.674%	$78.4943	$78.49	$78.50	$78.50
Purchase #2	$77.80	8.546%	$84.4488	$84.45	$84.45	$84.40
Purchase #3	$146.28	4.172%	$152.3828	$152.38	$152.40	$152.40
Purchase #4	$139.96	8.531%	$151.9	$151.90	$151.90	$151.90
Purchase #5	$96.27	10.776%	$106.6441	$106.64	$106.65	$106.60
Purchase #6	$65.70	6.280%	$69.826	$69.83	$69.85	$69.80
Purchase #7	$69.31	11.307%	$77.1469	$77.15	$77.15	$77.10
7 purchase totals =	$668.22		$720.8429	$720.84	$720.90	$720.70