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	$199.98	12.356%	$224.6895	$224.69	$224.70	$224.70
Purchase #2	$137.93	13.698%	$156.8237	$156.82	$156.80	$156.80
Purchase #3	$189.31	13.770%	$215.378	$215.38	$215.40	$215.40
Purchase #4	$190.88	10.720%	$211.3423	$211.34	$211.35	$211.30
Purchase #5	$79.36	12.195%	$89.038	$89.04	$89.05	$89.00
Purchase #6	$133.87	3.181%	$138.1284	$138.13	$138.15	$138.10
Purchase #7	$55.44	11.816%	$61.9908	$61.99	$62.00	$62.00
7 purchase totals =	$986.77		$1,097.3907	$1,097.39	$1,097.45	$1,097.30