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	$26.90	9.507%	$29.4574	$29.46	$29.45	$29.50
Purchase #2	$79.64	7.276%	$85.4346	$85.43	$85.45	$85.40
Purchase #3	$151.69	11.817%	$169.6152	$169.62	$169.60	$169.60
Purchase #4	$127.38	12.216%	$142.9407	$142.94	$142.95	$142.90
Purchase #5	$42.25	11.150%	$46.9609	$46.96	$46.95	$47.00
Purchase #6	$12.61	8.708%	$13.7081	$13.71	$13.70	$13.70
Purchase #7	$190.33	4.116%	$198.164	$198.16	$198.15	$198.20
7 purchase totals =	$630.80		$686.2809	$686.28	$686.25	$686.30