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	$188.71	8.394%	$204.5503	$204.55	$204.55	$204.60
Purchase #2	$107.75	5.711%	$113.9036	$113.90	$113.90	$113.90
Purchase #3	$120.28	6.572%	$128.1848	$128.18	$128.20	$128.20
Purchase #4	$56.40	5.696%	$59.6125	$59.61	$59.60	$59.60
Purchase #5	$73.45	7.399%	$78.8846	$78.88	$78.90	$78.90
Purchase #6	$19.83	9.634%	$21.7404	$21.74	$21.75	$21.70
Purchase #7	$29.38	8.659%	$31.924	$31.92	$31.90	$31.90
7 purchase totals =	$595.80		$638.8002	$638.78	$638.80	$638.80