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	$235.66	8.522%	$255.7429	$255.74	$255.75	$255.70
Purchase #2	$36.26	13.590%	$41.1877	$41.19	$41.20	$41.20
Purchase #3	$211.90	6.314%	$225.2794	$225.28	$225.30	$225.30
Purchase #4	$106.79	11.278%	$118.8338	$118.83	$118.85	$118.80
Purchase #5	$222.59	3.278%	$229.8865	$229.89	$229.90	$229.90
Purchase #6	$164.57	3.735%	$170.7167	$170.72	$170.70	$170.70
Purchase #7	$124.73	13.109%	$141.0809	$141.08	$141.10	$141.10
7 purchase totals =	$1,102.50		$1,182.7279	$1,182.73	$1,182.80	$1,182.70