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	$239.66	12.404%	$269.3874	$269.39	$269.40	$269.40
Purchase #2	$162.54	3.700%	$168.554	$168.55	$168.55	$168.60
Purchase #3	$200.86	9.390%	$219.7208	$219.72	$219.70	$219.70
Purchase #4	$215.38	6.806%	$230.0388	$230.04	$230.05	$230.00
Purchase #5	$59.30	13.529%	$67.3227	$67.32	$67.30	$67.30
Purchase #6	$69.86	6.573%	$74.4519	$74.45	$74.45	$74.50
Purchase #7	$109.67	13.843%	$124.8516	$124.85	$124.85	$124.90
7 purchase totals =	$1,057.27		$1,154.3272	$1,154.32	$1,154.30	$1,154.40