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	$149.90	3.571%	$155.2529	$155.25	$155.25	$155.30
Purchase #2	$20.81	9.585%	$22.8046	$22.80	$22.80	$22.80
Purchase #3	$214.54	11.640%	$239.5125	$239.51	$239.50	$239.50
Purchase #4	$28.96	12.465%	$32.5699	$32.57	$32.55	$32.60
Purchase #5	$231.73	10.723%	$256.5784	$256.58	$256.60	$256.60
Purchase #6	$65.54	9.640%	$71.8581	$71.86	$71.85	$71.90
Purchase #7	$223.38	8.401%	$242.1462	$242.15	$242.15	$242.10
7 purchase totals =	$934.86		$1,020.7226	$1,020.72	$1,020.70	$1,020.80