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	$57.68	3.162%	$59.5038	$59.50	$59.50	$59.50
Purchase #2	$73.88	7.473%	$79.4011	$79.40	$79.40	$79.40
Purchase #3	$92.77	8.627%	$100.7733	$100.77	$100.75	$100.80
Purchase #4	$96.37	12.459%	$108.3767	$108.38	$108.40	$108.40
Purchase #5	$72.27	11.711%	$80.7335	$80.73	$80.75	$80.70
Purchase #6	$51.67	9.198%	$56.4226	$56.42	$56.40	$56.40
Purchase #7	$229.25	3.463%	$237.1889	$237.19	$237.20	$237.20
7 purchase totals =	$673.89		$722.3999	$722.39	$722.40	$722.40