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	$57.75	3.598%	$59.8278	$59.83	$59.85	$59.80
Purchase #2	$104.52	7.433%	$112.289	$112.29	$112.30	$112.30
Purchase #3	$75.32	8.606%	$81.802	$81.80	$81.80	$81.80
Purchase #4	$130.88	6.592%	$139.5076	$139.51	$139.50	$139.50
Purchase #5	$162.98	9.230%	$178.0231	$178.02	$178.00	$178.00
Purchase #6	$22.31	12.595%	$25.1199	$25.12	$25.10	$25.10
Purchase #7	$45.47	12.671%	$51.2315	$51.23	$51.25	$51.20
7 purchase totals =	$599.23		$647.8009	$647.80	$647.80	$647.70