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	$71.90	12.628%	$80.9795	$80.98	$81.00	$81.00
Purchase #2	$149.52	12.628%	$168.4014	$168.40	$168.40	$168.40
Purchase #3	$105.72	5.279%	$111.301	$111.30	$111.30	$111.30
Purchase #4	$144.79	8.218%	$156.6888	$156.69	$156.70	$156.70
Purchase #5	$139.85	5.158%	$147.0635	$147.06	$147.05	$147.10
Purchase #6	$48.93	3.265%	$50.5276	$50.53	$50.55	$50.50
Purchase #7	$102.85	10.199%	$113.3397	$113.34	$113.35	$113.30
7 purchase totals =	$763.56		$828.3015	$828.30	$828.35	$828.30