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	$50.37	8.748%	$54.7764	$54.78	$54.80	$54.80
Purchase #2	$85.93	9.203%	$93.8381	$93.84	$93.85	$93.80
Purchase #3	$210.39	13.185%	$238.1299	$238.13	$238.15	$238.10
Purchase #4	$197.91	11.687%	$221.0397	$221.04	$221.05	$221.00
Purchase #5	$85.90	4.323%	$89.6135	$89.61	$89.60	$89.60
Purchase #6	$31.38	5.359%	$33.0617	$33.06	$33.05	$33.10
Purchase #7	$236.50	3.218%	$244.1106	$244.11	$244.10	$244.10
7 purchase totals =	$898.38		$974.5699	$974.57	$974.60	$974.50