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	$247.31	3.421%	$255.7705	$255.77	$255.75	$255.80
Purchase #2	$134.47	5.178%	$141.4329	$141.43	$141.45	$141.40
Purchase #3	$131.59	6.349%	$139.9446	$139.94	$139.95	$139.90
Purchase #4	$108.50	11.681%	$121.1739	$121.17	$121.15	$121.20
Purchase #5	$129.33	10.595%	$143.0325	$143.03	$143.05	$143.00
Purchase #6	$28.78	7.705%	$30.9975	$31.00	$31.00	$31.00
Purchase #7	$12.32	9.746%	$13.5207	$13.52	$13.50	$13.50
7 purchase totals =	$792.30		$845.8726	$845.86	$845.85	$845.80