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	$209.51	13.536%	$237.8693	$237.87	$237.85	$237.90
Purchase #2	$130.85	6.869%	$139.8381	$139.84	$139.85	$139.80
Purchase #3	$52.45	7.351%	$56.3056	$56.31	$56.30	$56.30
Purchase #4	$31.39	6.448%	$33.414	$33.41	$33.40	$33.40
Purchase #5	$204.40	7.230%	$219.1781	$219.18	$219.20	$219.20
Purchase #6	$75.81	9.122%	$82.7254	$82.73	$82.75	$82.70
Purchase #7	$45.35	13.549%	$51.4945	$51.49	$51.50	$51.50
7 purchase totals =	$749.76		$820.8250	$820.83	$820.85	$820.80