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	$230.70	12.139%	$258.7047	$258.70	$258.70	$258.70
Purchase #2	$53.35	8.441%	$57.8533	$57.85	$57.85	$57.90
Purchase #3	$18.43	10.330%	$20.3338	$20.33	$20.35	$20.30
Purchase #4	$25.35	5.841%	$26.8307	$26.83	$26.85	$26.80
Purchase #5	$125.56	4.700%	$131.4613	$131.46	$131.45	$131.50
Purchase #6	$184.90	3.645%	$191.6396	$191.64	$191.65	$191.60
Purchase #7	$103.74	10.585%	$114.7209	$114.72	$114.70	$114.70
7 purchase totals =	$742.03		$801.5443	$801.53	$801.55	$801.50