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	$46.41	13.491%	$52.6712	$52.67	$52.65	$52.70
Purchase #2	$202.69	9.735%	$222.4219	$222.42	$222.40	$222.40
Purchase #3	$105.96	3.768%	$109.9526	$109.95	$109.95	$110.00
Purchase #4	$182.43	4.619%	$190.8564	$190.86	$190.85	$190.90
Purchase #5	$179.78	9.422%	$196.7189	$196.72	$196.70	$196.70
Purchase #6	$99.56	9.293%	$108.8121	$108.81	$108.80	$108.80
Purchase #7	$100.29	8.372%	$108.6863	$108.69	$108.70	$108.70
7 purchase totals =	$917.12		$990.1194	$990.12	$990.05	$990.20