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	$166.90	3.483%	$172.7131	$172.71	$172.70	$172.70
Purchase #2	$40.29	12.132%	$45.178	$45.18	$45.20	$45.20
Purchase #3	$138.52	13.168%	$156.7603	$156.76	$156.75	$156.80
Purchase #4	$214.89	7.432%	$230.8606	$230.86	$230.85	$230.90
Purchase #5	$60.82	9.135%	$66.3759	$66.38	$66.40	$66.40
Purchase #6	$198.34	12.860%	$223.8465	$223.85	$223.85	$223.80
Purchase #7	$89.93	5.334%	$94.7269	$94.73	$94.75	$94.70
7 purchase totals =	$909.69		$990.4613	$990.47	$990.50	$990.50