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	$108.36	13.662%	$123.1641	$123.16	$123.15	$123.20
Purchase #2	$190.45	13.588%	$216.3283	$216.33	$216.35	$216.30
Purchase #3	$141.61	4.400%	$147.8408	$147.84	$147.85	$147.80
Purchase #4	$184.86	8.103%	$199.8392	$199.84	$199.85	$199.80
Purchase #5	$130.94	12.556%	$147.3808	$147.38	$147.40	$147.40
Purchase #6	$74.54	3.856%	$77.4143	$77.41	$77.40	$77.40
Purchase #7	$40.81	11.424%	$45.4721	$45.47	$45.45	$45.50
7 purchase totals =	$871.57		$957.4396	$957.43	$957.45	$957.40