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	$104.25	5.226%	$109.6981	$109.70	$109.70	$109.70
Purchase #2	$38.55	7.239%	$41.3406	$41.34	$41.35	$41.30
Purchase #3	$249.85	10.762%	$276.7389	$276.74	$276.75	$276.70
Purchase #4	$136.45	11.727%	$152.4515	$152.45	$152.45	$152.50
Purchase #5	$82.25	9.631%	$90.1715	$90.17	$90.15	$90.20
Purchase #6	$89.65	11.130%	$99.628	$99.63	$99.65	$99.60
Purchase #7	$236.94	3.671%	$245.6381	$245.64	$245.65	$245.60
7 purchase totals =	$937.94		$1,015.6667	$1,015.67	$1,015.70	$1,015.60