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	$68.74	10.155%	$75.7205	$75.72	$75.70	$75.70
Purchase #2	$150.27	3.102%	$154.9314	$154.93	$154.95	$154.90
Purchase #3	$72.77	10.705%	$80.56	$80.56	$80.55	$80.60
Purchase #4	$144.56	8.325%	$156.5946	$156.59	$156.60	$156.60
Purchase #5	$62.36	12.627%	$70.2342	$70.23	$70.25	$70.20
Purchase #6	$204.75	5.432%	$215.872	$215.87	$215.85	$215.90
Purchase #7	$211.85	5.108%	$222.6713	$222.67	$222.65	$222.70
7 purchase totals =	$915.30		$976.5840	$976.57	$976.55	$976.60