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	$85.73	4.135%	$89.2749	$89.27	$89.25	$89.30
Purchase #2	$155.48	8.653%	$168.9337	$168.93	$168.95	$168.90
Purchase #3	$109.70	4.468%	$114.6014	$114.60	$114.60	$114.60
Purchase #4	$224.45	9.276%	$245.27	$245.27	$245.25	$245.30
Purchase #5	$210.65	12.866%	$237.7522	$237.75	$237.75	$237.80
Purchase #6	$134.61	10.311%	$148.4896	$148.49	$148.50	$148.50
Purchase #7	$208.49	13.479%	$236.5924	$236.59	$236.60	$236.60
7 purchase totals =	$1,129.11		$1,240.9142	$1,240.90	$1,240.90	$1,241.00