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	$51.56	10.848%	$57.1532	$57.15	$57.15	$57.20
Purchase #2	$149.50	10.657%	$165.4322	$165.43	$165.45	$165.40
Purchase #3	$56.31	8.751%	$61.2377	$61.24	$61.25	$61.20
Purchase #4	$209.41	9.528%	$229.3626	$229.36	$229.35	$229.40
Purchase #5	$32.53	13.287%	$36.8523	$36.85	$36.85	$36.90
Purchase #6	$103.43	5.713%	$109.339	$109.34	$109.35	$109.30
Purchase #7	$49.94	9.277%	$54.5729	$54.57	$54.55	$54.60
7 purchase totals =	$652.68		$713.9499	$713.94	$713.95	$714.00