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	$40.52	4.583%	$42.377	$42.38	$42.40	$42.40
Purchase #2	$84.56	4.413%	$88.2916	$88.29	$88.30	$88.30
Purchase #3	$234.67	11.850%	$262.4784	$262.48	$262.50	$262.50
Purchase #4	$131.57	3.591%	$136.2947	$136.29	$136.30	$136.30
Purchase #5	$137.93	4.621%	$144.3037	$144.30	$144.30	$144.30
Purchase #6	$218.41	8.320%	$236.5817	$236.58	$236.60	$236.60
Purchase #7	$30.75	6.573%	$32.7712	$32.77	$32.75	$32.80
7 purchase totals =	$878.41		$943.0983	$943.09	$943.15	$943.20