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	$93.77	7.455%	$100.7606	$100.76	$100.75	$100.80
Purchase #2	$225.56	4.261%	$235.1711	$235.17	$235.15	$235.20
Purchase #3	$131.89	4.263%	$137.5125	$137.51	$137.50	$137.50
Purchase #4	$218.46	8.495%	$237.0182	$237.02	$237.00	$237.00
Purchase #5	$19.41	9.166%	$21.1891	$21.19	$21.20	$21.20
Purchase #6	$86.67	4.494%	$90.5649	$90.56	$90.55	$90.60
Purchase #7	$188.53	10.710%	$208.7216	$208.72	$208.70	$208.70
7 purchase totals =	$964.29		$1,030.9380	$1,030.93	$1,030.85	$1,031.00