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	$85.74	3.650%	$88.8695	$88.87	$88.85	$88.90
Purchase #2	$103.32	8.816%	$112.4287	$112.43	$112.45	$112.40
Purchase #3	$117.33	9.604%	$128.5984	$128.60	$128.60	$128.60
Purchase #4	$182.72	9.466%	$200.0163	$200.02	$200.00	$200.00
Purchase #5	$150.70	6.136%	$159.947	$159.95	$159.95	$159.90
Purchase #6	$45.45	6.531%	$48.4183	$48.42	$48.40	$48.40
Purchase #7	$82.67	7.785%	$89.1059	$89.11	$89.10	$89.10
7 purchase totals =	$767.93		$827.3841	$827.40	$827.35	$827.30