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	$53.91	6.646%	$57.4929	$57.49	$57.50	$57.50
Purchase #2	$19.57	6.161%	$20.7757	$20.78	$20.80	$20.80
Purchase #3	$232.75	7.215%	$249.5429	$249.54	$249.55	$249.50
Purchase #4	$95.65	6.154%	$101.5363	$101.54	$101.55	$101.50
Purchase #5	$166.55	4.827%	$174.5894	$174.59	$174.60	$174.60
Purchase #6	$141.48	5.160%	$148.7804	$148.78	$148.80	$148.80
Purchase #7	$44.64	13.459%	$50.6481	$50.65	$50.65	$50.60
7 purchase totals =	$754.55		$803.3657	$803.37	$803.45	$803.30