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	$185.73	12.556%	$209.0503	$209.05	$209.05	$209.10
Purchase #2	$128.84	11.277%	$143.3693	$143.37	$143.35	$143.40
Purchase #3	$47.58	6.643%	$50.7407	$50.74	$50.75	$50.70
Purchase #4	$83.39	9.837%	$91.5931	$91.59	$91.60	$91.60
Purchase #5	$19.43	10.714%	$21.5117	$21.51	$21.50	$21.50
Purchase #6	$13.81	5.700%	$14.5972	$14.60	$14.60	$14.60
Purchase #7	$115.53	3.502%	$119.5759	$119.58	$119.60	$119.60
7 purchase totals =	$594.31		$650.4382	$650.44	$650.45	$650.50