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	$57.44	7.555%	$61.7796	$61.78	$61.80	$61.80
Purchase #2	$138.25	3.103%	$142.5399	$142.54	$142.55	$142.50
Purchase #3	$194.93	8.170%	$210.8558	$210.86	$210.85	$210.90
Purchase #4	$139.38	8.765%	$151.5967	$151.60	$151.60	$151.60
Purchase #5	$137.58	4.550%	$143.8399	$143.84	$143.85	$143.80
Purchase #6	$108.72	6.197%	$115.4574	$115.46	$115.45	$115.50
Purchase #7	$30.38	4.473%	$31.7389	$31.74	$31.75	$31.70
7 purchase totals =	$806.68		$857.8082	$857.82	$857.85	$857.80