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	$135.56	12.712%	$152.7924	$152.79	$152.80	$152.80
Purchase #2	$173.74	9.291%	$189.8822	$189.88	$189.90	$189.90
Purchase #3	$193.87	12.564%	$218.2278	$218.23	$218.25	$218.20
Purchase #4	$199.79	10.423%	$220.6141	$220.61	$220.60	$220.60
Purchase #5	$101.44	3.870%	$105.3657	$105.37	$105.35	$105.40
Purchase #6	$35.45	6.768%	$37.8493	$37.85	$37.85	$37.80
Purchase #7	$147.60	12.419%	$165.9304	$165.93	$165.95	$165.90
7 purchase totals =	$987.45		$1,090.6619	$1,090.66	$1,090.70	$1,090.60