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	$168.35	6.859%	$179.8971	$179.90	$179.90	$179.90
Purchase #2	$101.51	7.420%	$109.042	$109.04	$109.05	$109.00
Purchase #3	$84.60	11.725%	$94.5194	$94.52	$94.50	$94.50
Purchase #4	$32.50	9.342%	$35.5362	$35.54	$35.55	$35.50
Purchase #5	$237.67	8.802%	$258.5897	$258.59	$258.60	$258.60
Purchase #6	$110.87	12.325%	$124.5347	$124.53	$124.55	$124.50
Purchase #7	$47.64	13.410%	$54.0285	$54.03	$54.05	$54.00
7 purchase totals =	$783.14		$856.1476	$856.15	$856.20	$856.00