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	$94.59	13.667%	$107.5176	$107.52	$107.50	$107.50
Purchase #2	$47.95	4.800%	$50.2516	$50.25	$50.25	$50.30
Purchase #3	$148.59	12.196%	$166.712	$166.71	$166.70	$166.70
Purchase #4	$110.49	12.628%	$124.4427	$124.44	$124.45	$124.40
Purchase #5	$82.78	13.701%	$94.1217	$94.12	$94.10	$94.10
Purchase #6	$97.59	7.552%	$104.96	$104.96	$104.95	$105.00
Purchase #7	$137.28	3.354%	$141.8844	$141.88	$141.90	$141.90
7 purchase totals =	$719.27		$789.8900	$789.88	$789.85	$789.90