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	$134.88	12.349%	$151.5363	$151.54	$151.55	$151.50
Purchase #2	$166.39	12.102%	$186.5265	$186.53	$186.55	$186.50
Purchase #3	$70.83	6.555%	$75.4729	$75.47	$75.45	$75.50
Purchase #4	$17.26	4.827%	$18.0931	$18.09	$18.10	$18.10
Purchase #5	$83.36	7.456%	$89.5753	$89.58	$89.60	$89.60
Purchase #6	$236.29	8.731%	$256.9205	$256.92	$256.90	$256.90
Purchase #7	$67.81	9.788%	$74.4472	$74.45	$74.45	$74.40
7 purchase totals =	$776.82		$852.5718	$852.58	$852.60	$852.50