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	$62.55	9.588%	$68.5473	$68.55	$68.55	$68.50
Purchase #2	$19.78	6.823%	$21.1296	$21.13	$21.15	$21.10
Purchase #3	$141.93	6.318%	$150.8971	$150.90	$150.90	$150.90
Purchase #4	$122.50	12.315%	$137.5859	$137.59	$137.60	$137.60
Purchase #5	$159.55	3.148%	$164.5726	$164.57	$164.55	$164.60
Purchase #6	$139.63	7.326%	$149.8593	$149.86	$149.85	$149.90
Purchase #7	$191.36	4.146%	$199.2938	$199.29	$199.30	$199.30
7 purchase totals =	$837.30		$891.8856	$891.89	$891.90	$891.90