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	$115.85	10.842%	$128.4105	$128.41	$128.40	$128.40
Purchase #2	$209.61	11.859%	$234.4676	$234.47	$234.45	$234.50
Purchase #3	$30.88	5.315%	$32.5213	$32.52	$32.50	$32.50
Purchase #4	$17.31	4.645%	$18.114	$18.11	$18.10	$18.10
Purchase #5	$183.27	7.402%	$196.8356	$196.84	$196.85	$196.80
Purchase #6	$64.75	5.383%	$68.2355	$68.24	$68.25	$68.20
Purchase #7	$47.86	13.515%	$54.3283	$54.33	$54.35	$54.30
7 purchase totals =	$669.53		$732.9128	$732.92	$732.90	$732.80