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	$93.56	7.821%	$100.8773	$100.88	$100.90	$100.90
Purchase #2	$49.95	8.493%	$54.1923	$54.19	$54.20	$54.20
Purchase #3	$52.86	5.273%	$55.6473	$55.65	$55.65	$55.60
Purchase #4	$203.29	8.143%	$219.8439	$219.84	$219.85	$219.80
Purchase #5	$83.58	11.679%	$93.3413	$93.34	$93.35	$93.30
Purchase #6	$28.69	11.581%	$32.0126	$32.01	$32.00	$32.00
Purchase #7	$232.82	13.630%	$264.5534	$264.55	$264.55	$264.60
7 purchase totals =	$744.75		$820.4681	$820.46	$820.50	$820.40