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	$140.84	6.848%	$150.4847	$150.48	$150.50	$150.50
Purchase #2	$217.94	8.806%	$237.1318	$237.13	$237.15	$237.10
Purchase #3	$84.59	6.317%	$89.9336	$89.93	$89.95	$89.90
Purchase #4	$213.47	3.480%	$220.8988	$220.90	$220.90	$220.90
Purchase #5	$37.52	13.518%	$42.592	$42.59	$42.60	$42.60
Purchase #6	$125.85	12.483%	$141.5599	$141.56	$141.55	$141.60
Purchase #7	$249.51	6.154%	$264.8648	$264.86	$264.85	$264.90
7 purchase totals =	$1,069.72		$1,147.4656	$1,147.45	$1,147.50	$1,147.50