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	$52.25	4.748%	$54.7308	$54.73	$54.75	$54.70
Purchase #2	$151.38	13.693%	$172.1085	$172.11	$172.10	$172.10
Purchase #3	$72.61	7.317%	$77.9229	$77.92	$77.90	$77.90
Purchase #4	$48.70	13.163%	$55.1104	$55.11	$55.10	$55.10
Purchase #5	$177.36	9.706%	$194.5746	$194.57	$194.55	$194.60
Purchase #6	$43.37	9.495%	$47.488	$47.49	$47.50	$47.50
Purchase #7	$105.38	3.481%	$109.0483	$109.05	$109.05	$109.00
7 purchase totals =	$651.05		$710.9835	$710.98	$710.95	$710.90