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	$144.87	8.297%	$156.8899	$156.89	$156.90	$156.90
Purchase #2	$103.77	12.343%	$116.5783	$116.58	$116.60	$116.60
Purchase #3	$247.93	11.230%	$275.7725	$275.77	$275.75	$275.80
Purchase #4	$144.45	8.758%	$157.1009	$157.10	$157.10	$157.10
Purchase #5	$100.57	3.863%	$104.455	$104.46	$104.45	$104.50
Purchase #6	$180.30	11.735%	$201.4582	$201.46	$201.45	$201.50
Purchase #7	$123.94	7.586%	$133.3421	$133.34	$133.35	$133.30
7 purchase totals =	$1,045.83		$1,145.5969	$1,145.60	$1,145.60	$1,145.70