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	$248.44	3.387%	$256.8547	$256.85	$256.85	$256.90
Purchase #2	$90.28	10.237%	$99.522	$99.52	$99.50	$99.50
Purchase #3	$190.74	6.750%	$203.615	$203.62	$203.60	$203.60
Purchase #4	$180.50	5.446%	$190.33	$190.33	$190.35	$190.30
Purchase #5	$122.90	4.106%	$127.9463	$127.95	$127.95	$127.90
Purchase #6	$80.93	13.482%	$91.841	$91.84	$91.85	$91.80
Purchase #7	$137.37	9.540%	$150.4751	$150.48	$150.50	$150.50
7 purchase totals =	$1,051.16		$1,120.5841	$1,120.59	$1,120.60	$1,120.50