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	$137.74	9.164%	$150.3625	$150.36	$150.35	$150.40
Purchase #2	$52.45	13.753%	$59.6634	$59.66	$59.65	$59.70
Purchase #3	$115.51	6.154%	$122.6185	$122.62	$122.60	$122.60
Purchase #4	$110.79	11.401%	$123.4212	$123.42	$123.40	$123.40
Purchase #5	$84.57	10.780%	$93.6866	$93.69	$93.70	$93.70
Purchase #6	$220.89	13.405%	$250.5003	$250.50	$250.50	$250.50
Purchase #7	$139.74	13.371%	$158.4246	$158.42	$158.40	$158.40
7 purchase totals =	$861.69		$958.6771	$958.67	$958.60	$958.70