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	$73.77	13.614%	$83.813	$83.81	$83.80	$83.80
Purchase #2	$60.98	6.781%	$65.1151	$65.12	$65.10	$65.10
Purchase #3	$250.45	10.382%	$276.4517	$276.45	$276.45	$276.50
Purchase #4	$77.47	7.802%	$83.5142	$83.51	$83.50	$83.50
Purchase #5	$33.71	5.156%	$35.4481	$35.45	$35.45	$35.40
Purchase #6	$170.54	9.342%	$186.4718	$186.47	$186.45	$186.50
Purchase #7	$139.85	13.332%	$158.4948	$158.49	$158.50	$158.50
7 purchase totals =	$806.77		$889.3087	$889.30	$889.25	$889.30