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	$7.98	12.552%	$8.9816	$8.98	$9.00	$9.00
Purchase #2	$115.98	12.198%	$130.1272	$130.13	$130.15	$130.10
Purchase #3	$52.63	9.723%	$57.7472	$57.75	$57.75	$57.70
Purchase #4	$65.61	10.473%	$72.4813	$72.48	$72.50	$72.50
Purchase #5	$71.89	9.497%	$78.7174	$78.72	$78.70	$78.70
Purchase #6	$53.99	13.204%	$61.1188	$61.12	$61.10	$61.10
Purchase #7	$181.72	3.412%	$187.9203	$187.92	$187.90	$187.90
7 purchase totals =	$549.80		$597.0938	$597.10	$597.10	$597.00