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	$137.97	4.822%	$144.6229	$144.62	$144.60	$144.60
Purchase #2	$101.64	9.417%	$111.2114	$111.21	$111.20	$111.20
Purchase #3	$79.74	12.605%	$89.7912	$89.79	$89.80	$89.80
Purchase #4	$90.49	5.300%	$95.286	$95.29	$95.30	$95.30
Purchase #5	$116.88	4.161%	$121.7434	$121.74	$121.75	$121.70
Purchase #6	$231.63	8.119%	$250.436	$250.44	$250.45	$250.40
Purchase #7	$190.47	13.704%	$216.572	$216.57	$216.55	$216.60
7 purchase totals =	$948.82		$1,029.6629	$1,029.66	$1,029.65	$1,029.60