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	$111.28	10.707%	$123.1947	$123.19	$123.20	$123.20
Purchase #2	$58.69	9.692%	$64.3782	$64.38	$64.40	$64.40
Purchase #3	$174.72	13.814%	$198.8558	$198.86	$198.85	$198.90
Purchase #4	$32.53	9.516%	$35.6256	$35.63	$35.65	$35.60
Purchase #5	$133.79	4.683%	$140.0554	$140.06	$140.05	$140.10
Purchase #6	$31.37	6.262%	$33.3344	$33.33	$33.35	$33.30
Purchase #7	$158.50	10.393%	$174.9729	$174.97	$174.95	$175.00
7 purchase totals =	$700.88		$770.4170	$770.42	$770.45	$770.50