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	$105.78	3.593%	$109.5807	$109.58	$109.60	$109.60
Purchase #2	$40.80	9.342%	$44.6115	$44.61	$44.60	$44.60
Purchase #3	$239.52	12.557%	$269.5965	$269.60	$269.60	$269.60
Purchase #4	$169.58	5.855%	$179.5089	$179.51	$179.50	$179.50
Purchase #5	$20.85	3.433%	$21.5658	$21.57	$21.55	$21.60
Purchase #6	$64.30	9.234%	$70.2375	$70.24	$70.25	$70.20
Purchase #7	$215.86	11.248%	$240.1399	$240.14	$240.15	$240.10
7 purchase totals =	$856.69		$935.2408	$935.25	$935.25	$935.20