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	$30.82	3.466%	$31.8882	$31.89	$31.90	$31.90
Purchase #2	$178.93	4.432%	$186.8602	$186.86	$186.85	$186.90
Purchase #3	$42.44	11.560%	$47.3461	$47.35	$47.35	$47.30
Purchase #4	$96.52	10.252%	$106.4152	$106.42	$106.40	$106.40
Purchase #5	$50.76	6.583%	$54.1015	$54.10	$54.10	$54.10
Purchase #6	$211.39	4.746%	$221.4226	$221.42	$221.40	$221.40
Purchase #7	$141.27	12.510%	$158.9429	$158.94	$158.95	$158.90
7 purchase totals =	$752.13		$806.9767	$806.98	$806.95	$806.90