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	$83.84	8.272%	$90.7752	$90.78	$90.80	$90.80
Purchase #2	$180.45	9.564%	$197.7082	$197.71	$197.70	$197.70
Purchase #3	$66.46	6.588%	$70.8384	$70.84	$70.85	$70.80
Purchase #4	$178.38	7.203%	$191.2287	$191.23	$191.25	$191.20
Purchase #5	$92.43	4.439%	$96.533	$96.53	$96.55	$96.50
Purchase #6	$47.89	13.351%	$54.2838	$54.28	$54.30	$54.30
Purchase #7	$98.46	7.189%	$105.5383	$105.54	$105.55	$105.50
7 purchase totals =	$747.91		$806.9056	$806.91	$807.00	$806.80