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	$163.72	4.788%	$171.5589	$171.56	$171.55	$171.60
Purchase #2	$132.34	13.558%	$150.2827	$150.28	$150.30	$150.30
Purchase #3	$69.49	4.325%	$72.4954	$72.50	$72.50	$72.50
Purchase #4	$166.90	7.666%	$179.6946	$179.69	$179.70	$179.70
Purchase #5	$169.60	11.797%	$189.6077	$189.61	$189.60	$189.60
Purchase #6	$72.67	5.364%	$76.568	$76.57	$76.55	$76.60
Purchase #7	$139.53	8.738%	$151.7221	$151.72	$151.70	$151.70
7 purchase totals =	$914.25		$991.9294	$991.93	$991.90	$992.00