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	$7.30	7.654%	$7.8587	$7.86	$7.85	$7.90
Purchase #2	$174.33	5.124%	$183.2627	$183.26	$183.25	$183.30
Purchase #3	$170.29	12.243%	$191.1386	$191.14	$191.15	$191.10
Purchase #4	$235.65	8.113%	$254.7683	$254.77	$254.75	$254.80
Purchase #5	$103.34	10.758%	$114.4573	$114.46	$114.45	$114.50
Purchase #6	$229.86	10.810%	$254.7079	$254.71	$254.70	$254.70
Purchase #7	$119.85	9.317%	$131.0164	$131.02	$131.00	$131.00
7 purchase totals =	$1,040.62		$1,137.2099	$1,137.22	$1,137.15	$1,137.30