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	$14.31	13.874%	$16.2954	$16.30	$16.30	$16.30
Purchase #2	$34.65	10.479%	$38.281	$38.28	$38.30	$38.30
Purchase #3	$94.62	10.689%	$104.7339	$104.73	$104.75	$104.70
Purchase #4	$78.99	13.643%	$89.7666	$89.77	$89.75	$89.80
Purchase #5	$80.38	12.802%	$90.6702	$90.67	$90.65	$90.70
Purchase #6	$125.49	12.232%	$140.8399	$140.84	$140.85	$140.80
Purchase #7	$81.90	10.328%	$90.3586	$90.36	$90.35	$90.40
7 purchase totals =	$510.34		$570.9456	$570.95	$570.95	$571.00