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	$245.88	13.148%	$278.2083	$278.21	$278.20	$278.20
Purchase #2	$243.59	11.549%	$271.7222	$271.72	$271.70	$271.70
Purchase #3	$53.30	4.389%	$55.6393	$55.64	$55.65	$55.60
Purchase #4	$75.83	10.241%	$83.5958	$83.60	$83.60	$83.60
Purchase #5	$27.43	6.523%	$29.2193	$29.22	$29.20	$29.20
Purchase #6	$171.88	7.856%	$185.3829	$185.38	$185.40	$185.40
Purchase #7	$53.68	7.436%	$57.6716	$57.67	$57.65	$57.70
7 purchase totals =	$871.59		$961.4394	$961.44	$961.40	$961.40