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	$47.48	9.867%	$52.1649	$52.16	$52.15	$52.20
Purchase #2	$162.89	8.432%	$176.6249	$176.62	$176.60	$176.60
Purchase #3	$215.61	8.216%	$233.3245	$233.32	$233.30	$233.30
Purchase #4	$216.29	3.497%	$223.8537	$223.85	$223.85	$223.90
Purchase #5	$119.76	12.284%	$134.4713	$134.47	$134.45	$134.50
Purchase #6	$10.54	10.168%	$11.6117	$11.61	$11.60	$11.60
Purchase #7	$124.57	13.561%	$141.4629	$141.46	$141.45	$141.50
7 purchase totals =	$897.14		$973.5139	$973.49	$973.40	$973.60