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	$106.70	5.592%	$112.6667	$112.67	$112.65	$112.70
Purchase #2	$51.48	6.672%	$54.9147	$54.91	$54.90	$54.90
Purchase #3	$150.86	9.862%	$165.7378	$165.74	$165.75	$165.70
Purchase #4	$99.28	10.383%	$109.5882	$109.59	$109.60	$109.60
Purchase #5	$143.44	13.529%	$162.846	$162.85	$162.85	$162.80
Purchase #6	$29.82	10.169%	$32.8524	$32.85	$32.85	$32.90
Purchase #7	$37.46	3.843%	$38.8996	$38.90	$38.90	$38.90
7 purchase totals =	$619.04		$677.5054	$677.51	$677.50	$677.50