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	$166.56	8.155%	$180.143	$180.14	$180.15	$180.10
Purchase #2	$216.84	3.208%	$223.7962	$223.80	$223.80	$223.80
Purchase #3	$211.89	4.704%	$221.8573	$221.86	$221.85	$221.90
Purchase #4	$189.84	3.612%	$196.697	$196.70	$196.70	$196.70
Purchase #5	$128.35	9.621%	$140.6986	$140.70	$140.70	$140.70
Purchase #6	$239.51	10.726%	$265.1998	$265.20	$265.20	$265.20
Purchase #7	$116.41	12.421%	$130.8693	$130.87	$130.85	$130.90
7 purchase totals =	$1,269.40		$1,359.2612	$1,359.27	$1,359.25	$1,359.30