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	$227.42	12.765%	$256.4502	$256.45	$256.45	$256.50
Purchase #2	$57.58	9.669%	$63.1474	$63.15	$63.15	$63.10
Purchase #3	$200.33	10.780%	$221.9256	$221.93	$221.95	$221.90
Purchase #4	$37.98	11.728%	$42.4343	$42.43	$42.45	$42.40
Purchase #5	$159.34	11.625%	$177.8633	$177.86	$177.85	$177.90
Purchase #6	$90.28	5.608%	$95.3429	$95.34	$95.35	$95.30
Purchase #7	$207.31	8.206%	$224.3219	$224.32	$224.30	$224.30
7 purchase totals =	$980.24		$1,081.4856	$1,081.48	$1,081.50	$1,081.40