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	$229.83	11.535%	$256.3409	$256.34	$256.35	$256.30
Purchase #2	$51.44	13.601%	$58.4364	$58.44	$58.45	$58.40
Purchase #3	$246.52	7.276%	$264.4568	$264.46	$264.45	$264.50
Purchase #4	$45.85	12.552%	$51.6051	$51.61	$51.60	$51.60
Purchase #5	$76.38	9.383%	$83.5467	$83.55	$83.55	$83.50
Purchase #6	$195.69	9.346%	$213.9792	$213.98	$214.00	$214.00
Purchase #7	$214.85	3.384%	$222.1205	$222.12	$222.10	$222.10
7 purchase totals =	$1,060.56		$1,150.4856	$1,150.50	$1,150.50	$1,150.40