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	$50.88	8.576%	$55.2435	$55.24	$55.25	$55.20
Purchase #2	$190.67	10.703%	$211.0774	$211.08	$211.10	$211.10
Purchase #3	$193.49	8.303%	$209.5555	$209.56	$209.55	$209.60
Purchase #4	$71.64	12.717%	$80.7505	$80.75	$80.75	$80.80
Purchase #5	$144.63	7.273%	$155.1489	$155.15	$155.15	$155.10
Purchase #6	$99.89	9.314%	$109.1938	$109.19	$109.20	$109.20
Purchase #7	$142.62	12.523%	$160.4803	$160.48	$160.50	$160.50
7 purchase totals =	$893.82		$981.4499	$981.45	$981.50	$981.50