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	$105.75	6.786%	$112.9262	$112.93	$112.95	$112.90
Purchase #2	$139.29	10.795%	$154.3264	$154.33	$154.35	$154.30
Purchase #3	$35.98	10.627%	$39.8036	$39.80	$39.80	$39.80
Purchase #4	$166.67	7.262%	$178.7736	$178.77	$178.75	$178.80
Purchase #5	$55.88	5.872%	$59.1613	$59.16	$59.15	$59.20
Purchase #6	$68.37	3.657%	$70.8703	$70.87	$70.85	$70.90
Purchase #7	$223.93	13.770%	$254.7652	$254.77	$254.75	$254.80
7 purchase totals =	$795.87		$870.6266	$870.63	$870.60	$870.70