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	$74.82	8.270%	$81.0076	$81.01	$81.00	$81.00
Purchase #2	$205.96	11.623%	$229.8987	$229.90	$229.90	$229.90
Purchase #3	$19.69	9.670%	$21.594	$21.59	$21.60	$21.60
Purchase #4	$112.57	11.867%	$125.9287	$125.93	$125.95	$125.90
Purchase #5	$134.82	6.521%	$143.6116	$143.61	$143.60	$143.60
Purchase #6	$174.33	9.380%	$190.6822	$190.68	$190.70	$190.70
Purchase #7	$250.72	9.345%	$274.1498	$274.15	$274.15	$274.10
7 purchase totals =	$972.91		$1,066.8726	$1,066.87	$1,066.90	$1,066.80