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	$126.98	10.109%	$139.8164	$139.82	$139.80	$139.80
Purchase #2	$48.30	12.205%	$54.195	$54.20	$54.20	$54.20
Purchase #3	$102.89	13.533%	$116.8141	$116.81	$116.80	$116.80
Purchase #4	$167.87	6.169%	$178.2259	$178.23	$178.25	$178.20
Purchase #5	$180.82	4.498%	$188.9533	$188.95	$188.95	$189.00
Purchase #6	$72.74	6.371%	$77.3743	$77.37	$77.35	$77.40
Purchase #7	$72.46	9.511%	$79.3517	$79.35	$79.35	$79.40
7 purchase totals =	$772.06		$834.7307	$834.73	$834.70	$834.80