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	$165.97	13.412%	$188.2299	$188.23	$188.25	$188.20
Purchase #2	$143.59	11.681%	$160.3627	$160.36	$160.35	$160.40
Purchase #3	$37.34	8.213%	$40.4067	$40.41	$40.40	$40.40
Purchase #4	$59.31	5.854%	$62.782	$62.78	$62.80	$62.80
Purchase #5	$91.30	11.176%	$101.5037	$101.50	$101.50	$101.50
Purchase #6	$64.83	13.550%	$73.6145	$73.61	$73.60	$73.60
Purchase #7	$218.47	5.568%	$230.6344	$230.63	$230.65	$230.60
7 purchase totals =	$780.81		$857.5339	$857.52	$857.55	$857.50