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	$205.54	12.760%	$231.7669	$231.77	$231.75	$231.80
Purchase #2	$236.40	10.335%	$260.8319	$260.83	$260.85	$260.80
Purchase #3	$17.73	7.866%	$19.1246	$19.12	$19.10	$19.10
Purchase #4	$76.69	11.437%	$85.461	$85.46	$85.45	$85.50
Purchase #5	$70.51	5.701%	$74.5298	$74.53	$74.55	$74.50
Purchase #6	$85.32	5.869%	$90.3274	$90.33	$90.35	$90.30
Purchase #7	$162.71	8.670%	$176.817	$176.82	$176.80	$176.80
7 purchase totals =	$854.90		$938.8586	$938.86	$938.85	$938.80