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	$99.82	12.340%	$112.1378	$112.14	$112.15	$112.10
Purchase #2	$225.63	6.636%	$240.6028	$240.60	$240.60	$240.60
Purchase #3	$148.76	13.754%	$169.2205	$169.22	$169.20	$169.20
Purchase #4	$151.78	9.554%	$166.2811	$166.28	$166.30	$166.30
Purchase #5	$162.61	5.248%	$171.1438	$171.14	$171.15	$171.10
Purchase #6	$68.69	13.556%	$78.0016	$78.00	$78.00	$78.00
Purchase #7	$218.39	12.228%	$245.0947	$245.09	$245.10	$245.10
7 purchase totals =	$1,075.68		$1,182.4823	$1,182.47	$1,182.50	$1,182.40