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	$134.43	3.504%	$139.1404	$139.14	$139.15	$139.10
Purchase #2	$168.77	11.360%	$187.9423	$187.94	$187.95	$187.90
Purchase #3	$238.27	7.277%	$255.6089	$255.61	$255.60	$255.60
Purchase #4	$203.76	12.573%	$229.3787	$229.38	$229.40	$229.40
Purchase #5	$50.28	6.496%	$53.5462	$53.55	$53.55	$53.50
Purchase #6	$46.66	10.441%	$51.5318	$51.53	$51.55	$51.50
Purchase #7	$104.71	9.511%	$114.669	$114.67	$114.65	$114.70
7 purchase totals =	$946.88		$1,031.8173	$1,031.82	$1,031.85	$1,031.70