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	$140.55	6.479%	$149.6562	$149.66	$149.65	$149.70
Purchase #2	$103.66	12.368%	$116.4807	$116.48	$116.50	$116.50
Purchase #3	$219.70	6.784%	$234.6044	$234.60	$234.60	$234.60
Purchase #4	$94.88	7.441%	$101.94	$101.94	$101.95	$101.90
Purchase #5	$82.89	9.566%	$90.8193	$90.82	$90.80	$90.80
Purchase #6	$148.53	6.444%	$158.1013	$158.10	$158.10	$158.10
Purchase #7	$95.68	3.236%	$98.7762	$98.78	$98.80	$98.80
7 purchase totals =	$885.89		$950.3781	$950.38	$950.40	$950.40