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	$89.99	11.669%	$100.4909	$100.49	$100.50	$100.50
Purchase #2	$153.91	9.406%	$168.3868	$168.39	$168.40	$168.40
Purchase #3	$170.49	9.559%	$186.7871	$186.79	$186.80	$186.80
Purchase #4	$61.96	3.423%	$64.0809	$64.08	$64.10	$64.10
Purchase #5	$99.95	12.465%	$112.4088	$112.41	$112.40	$112.40
Purchase #6	$82.80	3.373%	$85.5928	$85.59	$85.60	$85.60
Purchase #7	$47.75	13.318%	$54.1093	$54.11	$54.10	$54.10
7 purchase totals =	$706.85		$771.8566	$771.86	$771.90	$771.90