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	$227.68	5.508%	$240.2206	$240.22	$240.20	$240.20
Purchase #2	$242.93	9.301%	$265.5249	$265.52	$265.50	$265.50
Purchase #3	$150.60	13.585%	$171.059	$171.06	$171.05	$171.10
Purchase #4	$142.64	8.206%	$154.345	$154.35	$154.35	$154.30
Purchase #5	$83.52	13.635%	$94.908	$94.91	$94.90	$94.90
Purchase #6	$237.70	11.554%	$265.1639	$265.16	$265.15	$265.20
Purchase #7	$36.33	4.319%	$37.8991	$37.90	$37.90	$37.90
7 purchase totals =	$1,121.40		$1,229.1205	$1,229.12	$1,229.05	$1,229.10