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	$22.41	5.172%	$23.569	$23.57	$23.55	$23.60
Purchase #2	$91.40	9.684%	$100.2512	$100.25	$100.25	$100.30
Purchase #3	$83.93	8.693%	$91.226	$91.23	$91.25	$91.20
Purchase #4	$35.38	9.736%	$38.8246	$38.82	$38.80	$38.80
Purchase #5	$103.59	4.520%	$108.2723	$108.27	$108.25	$108.30
Purchase #6	$225.82	4.211%	$235.3293	$235.33	$235.35	$235.30
Purchase #7	$110.83	11.635%	$123.7251	$123.73	$123.75	$123.70
7 purchase totals =	$673.36		$721.1975	$721.20	$721.20	$721.20