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	$73.95	6.456%	$78.7242	$78.72	$78.70	$78.70
Purchase #2	$93.72	3.821%	$97.301	$97.30	$97.30	$97.30
Purchase #3	$218.71	4.692%	$228.9719	$228.97	$228.95	$229.00
Purchase #4	$130.35	9.824%	$143.1556	$143.16	$143.15	$143.20
Purchase #5	$75.61	10.315%	$83.4092	$83.41	$83.40	$83.40
Purchase #6	$133.66	12.760%	$150.715	$150.72	$150.70	$150.70
Purchase #7	$118.56	12.260%	$133.0955	$133.10	$133.10	$133.10
7 purchase totals =	$844.56		$915.3724	$915.38	$915.30	$915.40