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	$17.51	11.557%	$19.5336	$19.53	$19.55	$19.50
Purchase #2	$194.68	7.441%	$209.1661	$209.17	$209.15	$209.20
Purchase #3	$96.95	3.706%	$100.543	$100.54	$100.55	$100.50
Purchase #4	$172.76	10.400%	$190.727	$190.73	$190.75	$190.70
Purchase #5	$68.43	13.856%	$77.9117	$77.91	$77.90	$77.90
Purchase #6	$170.30	13.159%	$192.7098	$192.71	$192.70	$192.70
Purchase #7	$136.27	4.364%	$142.2168	$142.22	$142.20	$142.20
7 purchase totals =	$856.90		$932.8080	$932.81	$932.80	$932.70