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	$239.52	7.806%	$258.2169	$258.22	$258.20	$258.20
Purchase #2	$40.74	8.811%	$44.3296	$44.33	$44.35	$44.30
Purchase #3	$96.94	3.312%	$100.1507	$100.15	$100.15	$100.20
Purchase #4	$111.60	12.532%	$125.5857	$125.59	$125.60	$125.60
Purchase #5	$38.79	11.645%	$43.3071	$43.31	$43.30	$43.30
Purchase #6	$75.55	12.600%	$85.0693	$85.07	$85.05	$85.10
Purchase #7	$82.47	10.797%	$91.3743	$91.37	$91.35	$91.40
7 purchase totals =	$685.61		$748.0336	$748.04	$748.00	$748.10