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	$178.84	11.530%	$199.4603	$199.46	$199.45	$199.50
Purchase #2	$135.34	5.407%	$142.6578	$142.66	$142.65	$142.70
Purchase #3	$238.94	6.559%	$254.6121	$254.61	$254.60	$254.60
Purchase #4	$67.37	7.267%	$72.2658	$72.27	$72.25	$72.30
Purchase #5	$130.53	13.664%	$148.3656	$148.37	$148.35	$148.40
Purchase #6	$232.49	3.410%	$240.4179	$240.42	$240.40	$240.40
Purchase #7	$157.69	7.503%	$169.5215	$169.52	$169.50	$169.50
7 purchase totals =	$1,141.20		$1,227.3010	$1,227.31	$1,227.20	$1,227.40