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	$153.73	13.519%	$174.5128	$174.51	$174.50	$174.50
Purchase #2	$66.53	7.341%	$71.414	$71.41	$71.40	$71.40
Purchase #3	$51.86	12.744%	$58.469	$58.47	$58.45	$58.50
Purchase #4	$233.80	8.537%	$253.7595	$253.76	$253.75	$253.80
Purchase #5	$89.52	4.852%	$93.8635	$93.86	$93.85	$93.90
Purchase #6	$177.56	13.132%	$200.8772	$200.88	$200.90	$200.90
Purchase #7	$16.53	5.538%	$17.4454	$17.45	$17.45	$17.40
7 purchase totals =	$789.53		$870.3414	$870.34	$870.30	$870.40