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	$236.89	13.300%	$268.3964	$268.40	$268.40	$268.40
Purchase #2	$161.70	4.790%	$169.4454	$169.45	$169.45	$169.40
Purchase #3	$127.75	7.130%	$136.8586	$136.86	$136.85	$136.90
Purchase #4	$85.96	4.109%	$89.4921	$89.49	$89.50	$89.50
Purchase #5	$90.50	5.841%	$95.7861	$95.79	$95.80	$95.80
Purchase #6	$145.46	6.332%	$154.6705	$154.67	$154.65	$154.70
Purchase #7	$43.31	3.231%	$44.7093	$44.71	$44.70	$44.70
7 purchase totals =	$891.57		$959.3584	$959.37	$959.35	$959.40