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	$135.86	13.327%	$153.9661	$153.97	$153.95	$154.00
Purchase #2	$89.47	11.617%	$99.8637	$99.86	$99.85	$99.90
Purchase #3	$219.56	13.590%	$249.3982	$249.40	$249.40	$249.40
Purchase #4	$244.37	12.153%	$274.0683	$274.07	$274.05	$274.10
Purchase #5	$179.30	5.209%	$188.6397	$188.64	$188.65	$188.60
Purchase #6	$166.65	11.253%	$185.4031	$185.40	$185.40	$185.40
Purchase #7	$227.33	5.476%	$239.7786	$239.78	$239.80	$239.80
7 purchase totals =	$1,262.54		$1,391.1177	$1,391.12	$1,391.10	$1,391.20