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	$61.97	13.409%	$70.2796	$70.28	$70.30	$70.30
Purchase #2	$21.93	12.647%	$24.7035	$24.70	$24.70	$24.70
Purchase #3	$247.78	13.216%	$280.5266	$280.53	$280.55	$280.50
Purchase #4	$182.99	6.229%	$194.3884	$194.39	$194.40	$194.40
Purchase #5	$247.78	11.368%	$275.9476	$275.95	$275.95	$275.90
Purchase #6	$68.76	4.734%	$72.0151	$72.02	$72.00	$72.00
Purchase #7	$76.73	12.173%	$86.0703	$86.07	$86.05	$86.10
7 purchase totals =	$907.94		$1,003.9311	$1,003.94	$1,003.95	$1,003.90