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	$178.69	11.474%	$199.1929	$199.19	$199.20	$199.20
Purchase #2	$144.54	8.213%	$156.4111	$156.41	$156.40	$156.40
Purchase #3	$42.47	11.768%	$47.4679	$47.47	$47.45	$47.50
Purchase #4	$150.30	5.850%	$159.0926	$159.09	$159.10	$159.10
Purchase #5	$63.37	10.727%	$70.1677	$70.17	$70.15	$70.20
Purchase #6	$131.66	7.298%	$141.2685	$141.27	$141.25	$141.30
Purchase #7	$102.30	10.196%	$112.7305	$112.73	$112.75	$112.70
7 purchase totals =	$813.33		$886.3312	$886.33	$886.30	$886.40