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	$76.58	5.145%	$80.52	$80.52	$80.50	$80.50
Purchase #2	$93.34	10.816%	$103.4357	$103.44	$103.45	$103.40
Purchase #3	$229.97	11.188%	$255.699	$255.70	$255.70	$255.70
Purchase #4	$206.55	8.689%	$224.4971	$224.50	$224.50	$224.50
Purchase #5	$202.37	10.600%	$223.8212	$223.82	$223.80	$223.80
Purchase #6	$16.60	10.303%	$18.3103	$18.31	$18.30	$18.30
Purchase #7	$147.59	7.411%	$158.5279	$158.53	$158.55	$158.50
7 purchase totals =	$973.00		$1,064.8112	$1,064.82	$1,064.80	$1,064.70