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	$141.31	4.159%	$147.1871	$147.19	$147.20	$147.20
Purchase #2	$137.34	9.739%	$150.7155	$150.72	$150.70	$150.70
Purchase #3	$170.66	12.760%	$192.4362	$192.44	$192.45	$192.40
Purchase #4	$136.78	13.188%	$154.8185	$154.82	$154.80	$154.80
Purchase #5	$227.49	10.500%	$251.3765	$251.38	$251.40	$251.40
Purchase #6	$107.35	6.631%	$114.4684	$114.47	$114.45	$114.50
Purchase #7	$100.72	11.513%	$112.3159	$112.32	$112.30	$112.30
7 purchase totals =	$1,021.65		$1,123.3181	$1,123.34	$1,123.30	$1,123.30