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	$172.73	3.330%	$178.4819	$178.48	$178.50	$178.50
Purchase #2	$222.73	13.734%	$253.3197	$253.32	$253.30	$253.30
Purchase #3	$70.82	9.724%	$77.7065	$77.71	$77.70	$77.70
Purchase #4	$199.59	10.742%	$221.03	$221.03	$221.05	$221.00
Purchase #5	$189.55	3.710%	$196.5823	$196.58	$196.60	$196.60
Purchase #6	$188.62	5.783%	$199.5279	$199.53	$199.55	$199.50
Purchase #7	$62.26	5.817%	$65.8817	$65.88	$65.90	$65.90
7 purchase totals =	$1,106.30		$1,192.5300	$1,192.53	$1,192.60	$1,192.50