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	$90.46	10.438%	$99.9022	$99.90	$99.90	$99.90
Purchase #2	$135.71	5.500%	$143.1741	$143.17	$143.15	$143.20
Purchase #3	$178.52	12.405%	$200.6654	$200.67	$200.65	$200.70
Purchase #4	$247.45	9.234%	$270.2995	$270.30	$270.30	$270.30
Purchase #5	$180.83	11.845%	$202.2493	$202.25	$202.25	$202.20
Purchase #6	$133.53	8.244%	$144.5382	$144.54	$144.55	$144.50
Purchase #7	$144.50	13.547%	$164.0754	$164.08	$164.10	$164.10
7 purchase totals =	$1,111.00		$1,224.9041	$1,224.91	$1,224.90	$1,224.90