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	$243.71	5.278%	$256.573	$256.57	$256.55	$256.60
Purchase #2	$159.70	9.650%	$175.1111	$175.11	$175.10	$175.10
Purchase #3	$61.82	11.633%	$69.0115	$69.01	$69.00	$69.00
Purchase #4	$248.72	4.421%	$259.7159	$259.72	$259.70	$259.70
Purchase #5	$29.35	11.447%	$32.7097	$32.71	$32.70	$32.70
Purchase #6	$71.92	5.419%	$75.8173	$75.82	$75.80	$75.80
Purchase #7	$100.61	11.305%	$111.984	$111.98	$112.00	$112.00
7 purchase totals =	$915.83		$980.9225	$980.92	$980.85	$980.90