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	$170.35	12.547%	$191.7238	$191.72	$191.70	$191.70
Purchase #2	$103.72	5.314%	$109.2317	$109.23	$109.25	$109.20
Purchase #3	$68.52	8.865%	$74.5943	$74.59	$74.60	$74.60
Purchase #4	$105.93	8.814%	$115.2667	$115.27	$115.25	$115.30
Purchase #5	$156.58	9.866%	$172.0282	$172.03	$172.05	$172.00
Purchase #6	$154.96	10.306%	$170.9302	$170.93	$170.95	$170.90
Purchase #7	$67.64	6.839%	$72.2659	$72.27	$72.25	$72.30
7 purchase totals =	$827.70		$906.0408	$906.04	$906.05	$906.00