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	$12.45	3.603%	$12.8986	$12.90	$12.90	$12.90
Purchase #2	$161.94	9.231%	$176.8887	$176.89	$176.90	$176.90
Purchase #3	$120.25	12.697%	$135.5181	$135.52	$135.50	$135.50
Purchase #4	$55.38	11.728%	$61.875	$61.88	$61.90	$61.90
Purchase #5	$91.49	13.616%	$103.9473	$103.95	$103.95	$103.90
Purchase #6	$214.27	6.362%	$227.9019	$227.90	$227.90	$227.90
Purchase #7	$239.63	4.637%	$250.7416	$250.74	$250.75	$250.70
7 purchase totals =	$895.41		$969.7712	$969.78	$969.80	$969.70