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	$35.52	9.327%	$38.833	$38.83	$38.85	$38.80
Purchase #2	$85.69	4.612%	$89.642	$89.64	$89.65	$89.60
Purchase #3	$87.90	3.220%	$90.7304	$90.73	$90.75	$90.70
Purchase #4	$92.53	10.277%	$102.0393	$102.04	$102.05	$102.00
Purchase #5	$63.61	3.244%	$65.6735	$65.67	$65.65	$65.70
Purchase #6	$229.89	11.810%	$257.04	$257.04	$257.05	$257.00
Purchase #7	$27.62	10.857%	$30.6187	$30.62	$30.60	$30.60
7 purchase totals =	$622.76		$674.5769	$674.57	$674.60	$674.40