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	$99.56	3.488%	$103.0327	$103.03	$103.05	$103.00
Purchase #2	$18.28	11.105%	$20.31	$20.31	$20.30	$20.30
Purchase #3	$203.45	9.790%	$223.3678	$223.37	$223.35	$223.40
Purchase #4	$190.99	9.252%	$208.6604	$208.66	$208.65	$208.70
Purchase #5	$144.98	4.603%	$151.6534	$151.65	$151.65	$151.70
Purchase #6	$39.66	10.109%	$43.6692	$43.67	$43.65	$43.70
Purchase #7	$221.56	8.566%	$240.5388	$240.54	$240.55	$240.50
7 purchase totals =	$918.48		$991.2323	$991.23	$991.20	$991.30