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	$99.61	12.173%	$111.7355	$111.74	$111.75	$111.70
Purchase #2	$136.59	7.333%	$146.6061	$146.61	$146.60	$146.60
Purchase #3	$109.33	9.580%	$119.8038	$119.80	$119.80	$119.80
Purchase #4	$191.37	11.728%	$213.8139	$213.81	$213.80	$213.80
Purchase #5	$137.71	11.283%	$153.2478	$153.25	$153.25	$153.20
Purchase #6	$237.94	5.218%	$250.3557	$250.36	$250.35	$250.40
Purchase #7	$111.96	3.457%	$115.8305	$115.83	$115.85	$115.80
7 purchase totals =	$1,024.51		$1,111.3933	$1,111.40	$1,111.40	$1,111.30