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	$106.73	12.246%	$119.8002	$119.80	$119.80	$119.80
Purchase #2	$150.47	7.458%	$161.6921	$161.69	$161.70	$161.70
Purchase #3	$38.80	7.110%	$41.5587	$41.56	$41.55	$41.60
Purchase #4	$89.77	8.681%	$97.5629	$97.56	$97.55	$97.60
Purchase #5	$35.86	5.528%	$37.8423	$37.84	$37.85	$37.80
Purchase #6	$86.80	4.579%	$90.7746	$90.77	$90.75	$90.80
Purchase #7	$98.27	6.795%	$104.9474	$104.95	$104.95	$104.90
7 purchase totals =	$606.70		$654.1782	$654.17	$654.15	$654.20