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	$183.50	3.253%	$189.4693	$189.47	$189.45	$189.50
Purchase #2	$101.89	3.852%	$105.8148	$105.81	$105.80	$105.80
Purchase #3	$136.77	7.362%	$146.839	$146.84	$146.85	$146.80
Purchase #4	$7.94	3.601%	$8.2259	$8.23	$8.25	$8.20
Purchase #5	$100.32	11.533%	$111.8899	$111.89	$111.90	$111.90
Purchase #6	$132.61	6.646%	$141.4233	$141.42	$141.40	$141.40
Purchase #7	$154.70	3.588%	$160.2506	$160.25	$160.25	$160.30
7 purchase totals =	$817.73		$863.9128	$863.91	$863.90	$863.90