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	$71.52	8.814%	$77.8238	$77.82	$77.80	$77.80
Purchase #2	$242.53	7.249%	$260.111	$260.11	$260.10	$260.10
Purchase #3	$229.82	3.499%	$237.8614	$237.86	$237.85	$237.90
Purchase #4	$103.36	8.793%	$112.4484	$112.45	$112.45	$112.40
Purchase #5	$240.65	8.289%	$260.5975	$260.60	$260.60	$260.60
Purchase #6	$85.63	11.751%	$95.6924	$95.69	$95.70	$95.70
Purchase #7	$121.82	4.840%	$127.7161	$127.72	$127.70	$127.70
7 purchase totals =	$1,095.33		$1,172.2506	$1,172.25	$1,172.20	$1,172.20