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	$109.65	13.548%	$124.5054	$124.51	$124.50	$124.50
Purchase #2	$103.33	12.626%	$116.3764	$116.38	$116.40	$116.40
Purchase #3	$126.85	9.589%	$139.0136	$139.01	$139.00	$139.00
Purchase #4	$61.80	13.534%	$70.164	$70.16	$70.15	$70.20
Purchase #5	$172.93	7.281%	$185.521	$185.52	$185.50	$185.50
Purchase #6	$169.95	7.650%	$182.9512	$182.95	$182.95	$183.00
Purchase #7	$53.85	12.356%	$60.5037	$60.50	$60.50	$60.50
7 purchase totals =	$798.36		$879.0353	$879.03	$879.00	$879.10