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	$190.75	9.272%	$208.4363	$208.44	$208.45	$208.40
Purchase #2	$160.31	9.700%	$175.8601	$175.86	$175.85	$175.90
Purchase #3	$226.95	3.411%	$234.6913	$234.69	$234.70	$234.70
Purchase #4	$178.56	6.444%	$190.0664	$190.07	$190.05	$190.10
Purchase #5	$231.31	6.287%	$245.8525	$245.85	$245.85	$245.90
Purchase #6	$86.44	4.561%	$90.3825	$90.38	$90.40	$90.40
Purchase #7	$139.89	13.535%	$158.8241	$158.82	$158.80	$158.80
7 purchase totals =	$1,214.21		$1,304.1132	$1,304.11	$1,304.10	$1,304.20