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	$150.45	10.157%	$165.7312	$165.73	$165.75	$165.70
Purchase #2	$152.76	4.523%	$159.6693	$159.67	$159.65	$159.70
Purchase #3	$229.71	11.113%	$255.2377	$255.24	$255.25	$255.20
Purchase #4	$27.33	6.682%	$29.1562	$29.16	$29.15	$29.20
Purchase #5	$50.34	13.577%	$57.1747	$57.17	$57.15	$57.20
Purchase #6	$80.34	11.457%	$89.5446	$89.54	$89.55	$89.50
Purchase #7	$113.82	10.400%	$125.6573	$125.66	$125.65	$125.70
7 purchase totals =	$804.75		$882.1710	$882.17	$882.15	$882.20