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	$241.38	10.686%	$267.1739	$267.17	$267.15	$267.20
Purchase #2	$85.80	4.649%	$89.7888	$89.79	$89.80	$89.80
Purchase #3	$115.74	9.803%	$127.086	$127.09	$127.10	$127.10
Purchase #4	$53.80	4.804%	$56.3846	$56.38	$56.40	$56.40
Purchase #5	$75.45	3.755%	$78.2831	$78.28	$78.30	$78.30
Purchase #6	$40.29	8.524%	$43.7243	$43.72	$43.70	$43.70
Purchase #7	$16.77	12.421%	$18.853	$18.85	$18.85	$18.90
7 purchase totals =	$629.23		$681.2937	$681.28	$681.30	$681.40