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	$171.69	9.656%	$188.2684	$188.27	$188.25	$188.30
Purchase #2	$229.25	9.736%	$251.5698	$251.57	$251.55	$251.60
Purchase #3	$95.85	8.462%	$103.9608	$103.96	$103.95	$104.00
Purchase #4	$226.57	7.469%	$243.4925	$243.49	$243.50	$243.50
Purchase #5	$43.76	6.761%	$46.7186	$46.72	$46.70	$46.70
Purchase #6	$104.90	11.433%	$116.8932	$116.89	$116.90	$116.90
Purchase #7	$219.60	3.773%	$227.8855	$227.89	$227.90	$227.90
7 purchase totals =	$1,091.62		$1,178.7888	$1,178.79	$1,178.75	$1,178.90