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	$99.75	13.297%	$113.0138	$113.01	$113.00	$113.00
Purchase #2	$151.80	8.255%	$164.3311	$164.33	$164.35	$164.30
Purchase #3	$197.69	8.220%	$213.9401	$213.94	$213.95	$213.90
Purchase #4	$51.99	4.770%	$54.4699	$54.47	$54.45	$54.50
Purchase #5	$40.48	4.431%	$42.2737	$42.27	$42.25	$42.30
Purchase #6	$70.62	8.632%	$76.7159	$76.72	$76.70	$76.70
Purchase #7	$139.40	6.786%	$148.8597	$148.86	$148.85	$148.90
7 purchase totals =	$751.73		$813.6042	$813.60	$813.55	$813.60