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	$84.77	5.624%	$89.5375	$89.54	$89.55	$89.50
Purchase #2	$6.81	8.601%	$7.3957	$7.40	$7.40	$7.40
Purchase #3	$104.60	12.710%	$117.8947	$117.89	$117.90	$117.90
Purchase #4	$114.51	3.314%	$118.3049	$118.30	$118.30	$118.30
Purchase #5	$145.30	8.728%	$157.9818	$157.98	$158.00	$158.00
Purchase #6	$200.56	5.328%	$211.2458	$211.25	$211.25	$211.20
Purchase #7	$247.65	10.381%	$273.3585	$273.36	$273.35	$273.40
7 purchase totals =	$904.20		$975.7189	$975.72	$975.75	$975.70