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	$153.81	4.240%	$160.3315	$160.33	$160.35	$160.30
Purchase #2	$184.72	6.535%	$196.7915	$196.79	$196.80	$196.80
Purchase #3	$115.84	8.338%	$125.4987	$125.50	$125.50	$125.50
Purchase #4	$104.61	6.589%	$111.5028	$111.50	$111.50	$111.50
Purchase #5	$142.68	8.238%	$154.434	$154.43	$154.45	$154.40
Purchase #6	$100.93	4.568%	$105.5405	$105.54	$105.55	$105.50
Purchase #7	$153.71	8.323%	$166.5033	$166.50	$166.50	$166.50
7 purchase totals =	$956.30		$1,020.6023	$1,020.59	$1,020.65	$1,020.50