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	$131.53	9.147%	$143.561	$143.56	$143.55	$143.60
Purchase #2	$106.25	3.308%	$109.7648	$109.76	$109.75	$109.80
Purchase #3	$123.57	6.749%	$131.9097	$131.91	$131.90	$131.90
Purchase #4	$155.33	8.159%	$168.0034	$168.00	$168.00	$168.00
Purchase #5	$91.72	11.601%	$102.3604	$102.36	$102.35	$102.40
Purchase #6	$142.97	6.675%	$152.5132	$152.51	$152.50	$152.50
Purchase #7	$35.60	12.230%	$39.9539	$39.95	$39.95	$40.00
7 purchase totals =	$786.97		$848.0664	$848.05	$848.00	$848.20