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	$109.93	4.723%	$115.122	$115.12	$115.10	$115.10
Purchase #2	$224.55	11.755%	$250.9459	$250.95	$250.95	$250.90
Purchase #3	$193.48	3.325%	$199.9132	$199.91	$199.90	$199.90
Purchase #4	$55.32	12.390%	$62.1741	$62.17	$62.15	$62.20
Purchase #5	$137.54	4.552%	$143.8008	$143.80	$143.80	$143.80
Purchase #6	$133.82	6.410%	$142.3979	$142.40	$142.40	$142.40
Purchase #7	$30.86	8.564%	$33.5029	$33.50	$33.50	$33.50
7 purchase totals =	$885.50		$947.8568	$947.85	$947.80	$947.80