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	$227.61	8.850%	$247.7535	$247.75	$247.75	$247.80
Purchase #2	$137.28	7.320%	$147.3289	$147.33	$147.35	$147.30
Purchase #3	$143.56	11.553%	$160.1455	$160.15	$160.15	$160.10
Purchase #4	$94.34	6.719%	$100.6787	$100.68	$100.70	$100.70
Purchase #5	$94.60	6.597%	$100.8408	$100.84	$100.85	$100.80
Purchase #6	$138.98	8.576%	$150.8989	$150.90	$150.90	$150.90
Purchase #7	$12.34	4.719%	$12.9223	$12.92	$12.90	$12.90
7 purchase totals =	$848.71		$920.5686	$920.57	$920.60	$920.50