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	$166.78	11.216%	$185.486	$185.49	$185.50	$185.50
Purchase #2	$215.90	13.128%	$244.2434	$244.24	$244.25	$244.20
Purchase #3	$119.83	8.642%	$130.1857	$130.19	$130.20	$130.20
Purchase #4	$18.45	9.550%	$20.212	$20.21	$20.20	$20.20
Purchase #5	$59.62	9.840%	$65.4866	$65.49	$65.50	$65.50
Purchase #6	$227.55	5.640%	$240.3838	$240.38	$240.40	$240.40
Purchase #7	$213.85	13.566%	$242.8609	$242.86	$242.85	$242.90
7 purchase totals =	$1,021.98		$1,128.8584	$1,128.86	$1,128.90	$1,128.90