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	$37.85	3.482%	$39.1679	$39.17	$39.15	$39.20
Purchase #2	$74.27	10.268%	$81.896	$81.90	$81.90	$81.90
Purchase #3	$42.96	5.635%	$45.3808	$45.38	$45.40	$45.40
Purchase #4	$171.69	6.136%	$182.2249	$182.22	$182.20	$182.20
Purchase #5	$175.34	3.644%	$181.7294	$181.73	$181.75	$181.70
Purchase #6	$99.29	11.279%	$110.4889	$110.49	$110.50	$110.50
Purchase #7	$17.47	6.245%	$18.561	$18.56	$18.55	$18.60
7 purchase totals =	$618.87		$659.4489	$659.45	$659.45	$659.50