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	$122.52	11.867%	$137.0594	$137.06	$137.05	$137.10
Purchase #2	$240.56	6.317%	$255.7562	$255.76	$255.75	$255.80
Purchase #3	$164.74	9.228%	$179.9422	$179.94	$179.95	$179.90
Purchase #4	$105.39	4.313%	$109.9355	$109.94	$109.95	$109.90
Purchase #5	$151.54	8.516%	$164.4451	$164.45	$164.45	$164.40
Purchase #6	$248.60	10.538%	$274.7975	$274.80	$274.80	$274.80
Purchase #7	$195.83	12.515%	$220.3381	$220.34	$220.35	$220.30
7 purchase totals =	$1,229.18		$1,342.2740	$1,342.29	$1,342.30	$1,342.20