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	$11.33	13.663%	$12.878	$12.88	$12.90	$12.90
Purchase #2	$130.34	9.512%	$142.7379	$142.74	$142.75	$142.70
Purchase #3	$184.87	6.523%	$196.9291	$196.93	$196.95	$196.90
Purchase #4	$234.50	12.769%	$264.4433	$264.44	$264.45	$264.40
Purchase #5	$34.46	11.370%	$38.3781	$38.38	$38.40	$38.40
Purchase #6	$183.83	10.570%	$203.2608	$203.26	$203.25	$203.30
Purchase #7	$157.98	9.607%	$173.1571	$173.16	$173.15	$173.20
7 purchase totals =	$937.31		$1,031.7843	$1,031.79	$1,031.85	$1,031.80