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	$20.33	9.844%	$22.3313	$22.33	$22.35	$22.30
Purchase #2	$93.45	12.705%	$105.3228	$105.32	$105.30	$105.30
Purchase #3	$159.40	7.253%	$170.9613	$170.96	$170.95	$171.00
Purchase #4	$147.71	11.242%	$164.3156	$164.32	$164.30	$164.30
Purchase #5	$227.25	13.754%	$258.506	$258.51	$258.50	$258.50
Purchase #6	$100.98	8.256%	$109.3169	$109.32	$109.30	$109.30
Purchase #7	$124.63	6.276%	$132.4518	$132.45	$132.45	$132.50
7 purchase totals =	$873.75		$963.2057	$963.21	$963.15	$963.20