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	$20.92	4.529%	$21.8675	$21.87	$21.85	$21.90
Purchase #2	$90.95	13.603%	$103.3219	$103.32	$103.30	$103.30
Purchase #3	$121.40	9.821%	$133.3227	$133.32	$133.30	$133.30
Purchase #4	$192.56	5.139%	$202.4557	$202.46	$202.45	$202.50
Purchase #5	$248.41	11.207%	$276.2493	$276.25	$276.25	$276.20
Purchase #6	$74.27	11.362%	$82.7086	$82.71	$82.70	$82.70
Purchase #7	$89.72	12.871%	$101.2679	$101.27	$101.25	$101.30
7 purchase totals =	$838.23		$921.1936	$921.20	$921.10	$921.20